* 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
Shawn Tabrizi