* 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

* 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

* Use Weight instead of u32 everywhere

* Revert Weight declaration

* Fix benches

* 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