Delete indexing code

[franckc]

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 master branch

Description:

Large clean up of the bridge server code:

• Remove event handler + DB and Search indexing code since it is replaced by the new Node.js based EventListener.
• Delete ABI of old contracts since these have been replaced by marketplace contracts.
• Temporarily comment out mobile notification logic code until it gets upgraded to work with the stages that an offer goes thru as defined in the marketplace contracts.
• Update Readme to reflect that indexing is now out of the bridge server. Only attestations and mobile notification remain for now on the bridge server.