Allow a different contracts directory to be specified

[tyleryasaka]

Checklist:

• [x] Code contains relevant tests for the problem you are solving
• [x] Code has been formatted with autopep8 --in-place --recursive --a --a .
• [x] Ensure all new and existing tests pass
• [x] Update any relevant READMEs and docs
• [x] Submit to the develop branch instead of master

Description:

This allows us to use a different directory in development (such as the gitignored contracts_dev directory) so that the contracts can be symlinked with the origin-js contracts.