Flask RESTful

[tyleryasaka]

Checklist:

• [x] Code contains relevant tests for the problem you are solving
• [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:

Contains commits from https://github.com/OriginProtocol/bridge-server/pull/27 (would be easier to review/merge that first)

• Swaps out apilib in exchange for Flask-RESTful and Marshmallow (And yes, I did try the flask-marshmallow library. It doesn't provide the serialization and deserialization that we need.)
• Cleans up API interface to be as standard and implementation-agnostic as possible; this API should be able to be replicated in other frameworks (e.g. RoR, Node/Express).
• Creates documentation for the Attestations API.
• Have this code up and running on heroku if anyone wants to test it out: http://bridge-server-test.herokuapp.com/

Finishes https://github.com/OriginProtocol/bridge-server/issues/21, https://github.com/OriginProtocol/bridge-server/issues/22, https://github.com/OriginProtocol/bridge-server/issues/8, https://github.com/OriginProtocol/bridge-server/issues/9, https://github.com/OriginProtocol/bridge-server/issues/7, https://github.com/OriginProtocol/bridge-server/issues/3, https://github.com/OriginProtocol/bridge-server/issues/23

[Gzing]

@tyleryasaka is this still in WIP or should I test/review this and try it out on my local?

[tyleryasaka]

@Gzing It's ready for review!