feat(Call API): Should response with a room identifier

Before:
- The Call API required the API client to supply the room identifier

After:
- The Call API will generate a room identifier based on UUID v4 and using the JS implementation written by Robert Kieffer (https://github.com/broofa/node-uuid).

Breaking changes:
- The Room Controller will break since this API is changing.
fix(Room controller): able to receive room identifier response from API

Before:
- POST data to Call API should contained caller, callee, and roomId

After:
- POST data to Call API should contained only caller and callee. The client will receive a JSON response contained a room identifier.
Merge branch 'use-uuid-for-room-identifier' into 0.4.0-alpha.2