Fix ABI generator to correctly handle tables from other contracts

[aamirpashaa]

Fixes #198

Change Description

There was a problem in the ABI generator that added included singleton table structs from other contracts (included using header import or with eosio::contract tag) to the ABI, which was not intended. This PR fixes this problem, and the appropriate test case with the desired ABI has also been added.

API Changes

• API Changes

Documentation Additions

• Documentation Additions

[dimas1185]

note that your solution doesn't handle case when singleton will have non-table type and be defined in other contract.
here is solution that handles all cases I can think of:
#201

[ericpassmore]

Thanks for the contribution. Our engineering met and decided we wanted a fuller solution that optimized the ABI and worked on a class level. You can review and contribute to our work in PR #201 The solution posted here adds additional abi that may not be needed by the contract. For that reason we are closing this PR.