Support `get scope` to list scopes for a given table name (or not)

[abourget]

The new /v1/chain/get_table_by_scope endpoint allows us to query the scopes.

• [ ] Integrate into eos-go as an eos.API function.
• [ ] Add a get scope command to eosc.

Ref: https://github.com/EOSIO/eos/pull/5486