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
Remove mailman
Set Api::MessagesController to create messages with type Messages::Web
Add ReadReceipts
Add #mark_read to Message to create ReadReceipts
Merge pull request #48 from austinylin/wip-129-message-api-fixes

WIP 129 Message API Fixes
Remove assets and helpers from scaffolds.

They usually create extra files that don't fit with the project structure.
Merge pull request #49 from austinylin/remove-mailman-readme

Remove mailman
Merge branch 'wip-27-read-receipts' of https://github.com/austinylin/helpful-web into austinylin-wip-27-read-receipts

Conflicts:
	app/models/message.rb