* closes#7009
adds parity_verifySignature RPC method
* removed unneccesary into
* adds support for chain replay protected signatures
* corrected chain replay protection check
* corrected possible overflow
* added tests
* use checked_sub to prevent possible overflow
* use saturating_mul to prevent possible overflow
* changed method signature to accept r,s,v components
* added unit tests
* more tests
* refactored tests for better readability
moved verify_signature tests to live in the same file.
* removed unneccesary imports
* fixed PR grumbles
* fixed rsv notation
* fixed rsv notation
* renamed BasicAcount to RecoveredAccount, Support zero chain_id
* fixed compile errors
* fixed tests
* doc comment
