Assign unique storage names to pallets. (#5010)

* Assign unique storage names to pallets.

* Bump spec

* Upgrade logic for finality tracker (untested)

* Logic for migrating Identity (untested)

* Logic for migrating transaction-payment

* Fix tests

* Fix `decl_storage` build

* Contract -> Contracts

* Update Cargo.lock

* bump spec

* update migration

* Fix merge error

* Migration for contracts

* Remove serde

* Remove some illegal spaces and Options

* Fix types in identity.

* Minor variable rename

Co-authored-by: Gavin Wood <gavin@parity.io>