* Make `decl_error!` errors usable

This pr implements support for returning errors of different pallets in
a pallet. These errors need to be declared with `decl_error!`.

The pr changes the following:

- Each dispatchable function now returns a `DispatchResult` which is an
alias for `Result<(), DispatchError>`.
- `DispatchError` is an enum that has 4 variants:
  - `Other`: For storing string error messages
  - `CannotLookup`: Variant that is returned when something returns a
  `sp_runtime::LookupError`
  - `BadOrigin`: Variant that is returned for any kind of bad origin
  - `Module`: The error of a specific module. Contains the `index`,
  `error` and the `message`. The index is the index of the module in
  `construct_runtime!`. `error` is the index of the error in the error
  enum declared by `decl_error!`. `message` is the message to the error
  variant (this will not be encoded).
- `construct_runtime!` now creates a new struct `ModuleToIndex`. This
struct implements the trait `ModuleToIndex`.
- `frame_system::Trait` has a new associated type: `ModuleToIndex` that
expects the `ModuleToIndex` generated by `construct_runtime!`.
- All error strings returned in any module are being converted now to `DispatchError`.
- `BadOrigin` is the default error returned by any type that implements `EnsureOrigin`.

* Fix frame system benchmarks

* Dust moves from reserved <-> free if below ED

* Add dust information to `ReapedAccount` event

* Introduce `BalanceSet` event

* More cleanly written `set_balance` logic

* Rename: Phase 1.

* Unify codec.

* Fixing: Phase 2

* Fixing: Phase 3.

* Fixing: Phase 4.

* Fixing: Phase 5.

* Fixing: Phase 6.

* Fixing: Phase 7.

* Fixing: Phase 8. Tests

* Fixing: Phase 9. Tests!!!

* Fixing: Phase 10. Moar tests!

* Finally done!

* More fixes.

* Rename primitives:: to sp_core::

* Apply renames in finality-grandpa.

* Fix benches.

* Fix benches 2.

* Revert node-template.

* Fix frame-system in our modules.

* primitives/sr-io -> primitives/io

* fix

* rename

* runtime-io -> sp-io

* git mv

* fix ci

* remove package name

* fix

* fix

* try minimizing diff

* try minimizing diff again

* try minimizing diff again

* primitives/sr-std -> primitives/std

* fix

* fix conflict

* rstd -> sp-std

* git mv

* fix review

* fix merge

* Adding script for rename, could be applicable for nodes on top of it, too

* add stderr and gitlab ci features

* apply script

* fix now minor details in expected stderr

* Update the Cargo.lock

* fix name: sc-transaction -> sc-tracing

* fix rename in script, too

* Introduce `VestingCurrency` trait

* Return error if account already has vesting schedule

* Use Weight instead of u32 everywhere

* Revert Weight declaration

* Fix benches

* define slashing spans

* tests and pruning for slashing-spans record

* validators get slashed before nominators

* apply slash to nominators as well

* chill and end slashing spans

* actually perform slashes

* integration (tests failing)

* prune metadata

* fix compilation

* some tests for slashing and metadata garbage collection

* correctly pass session index to slash handler

* test span-max property for nominators and validators

* test that slashes are summed correctly

* reward value computation

* implement rewarding

* add comment about rewards

* do not adjust slash fraction in offences module

* fix offences tests

* remove unused new_offenders field

* update runtime version

* fix up some docs

* fix some CI failures

* remove no-std incompatible vec! invocation

* try to fix span-max rounding error

* Update srml/staking/src/slashing.rs

Fix type: winow -> window

Co-Authored-By: Tomasz Drwięga <[email protected]>

* slashes from prior spans don't kick validator again

* more information for nominators, suppression

* ensure ledger is consistent with itself post-slash

* implement slash out of unlocking funds also

* slashing: create records to be applied after-the-fact

* queue slashes for a few eras later

* method for canceling deferred slashes

* attempt to fix test in CI

* storage migration for `Nominators`

* update node-runtime to use SlashDeferDuration

* adjust migration entry-points somewhat

* fix migration compilation

* add manual Vec import to migration

* enable migrations feature in node-runtime

* bump runtime version

* update to latest master crate renames

* update to use ensure-origin

* Apply suggestions from code review

use `ensure!`

Co-Authored-By: Gavin Wood <[email protected]>

* fix multi-slash removal

* initialize storage version to current in genesis

* add test for version initialization

* palette -> frame

* PALETTE, Palette -> FRAME

* Move folder pallete -> frame

* Update docs/Structure.adoc

Co-Authored-By: Benjamin Kampmann <[email protected]>

* Update docs/README.adoc

Co-Authored-By: Benjamin Kampmann <[email protected]>

* Update README.adoc