Account getters are removed from client context. x/auth has the
queriers necessary for retrieving account information.
These functions should be removed since they are currently
redundant and don't provide any extra value.
Closes: #4543
New Signature interface available in the top level types package.
auth.StdSignature implements such interface. User defined auth
module can now define their own custom signature types.
Work carried out in the context of the following issues:
- #4488
- #4487