Cleanup references to Supportly
Clarify relation/validations between message, conversation, and account

- Add accepts_nested_attributes_for :conversation to Message
- Require :account on Conversation
- Use FactoryGirl in conversation_test to handle account being required
Cleanup Api::MessagesController and add tests
Support the new account parameter in embed.js
Set Api::MessagesController to create messages with type Messages::Web
Merge pull request #48 from austinylin/wip-129-message-api-fixes

WIP 129 Message API Fixes