Remove dead code.
Change Conversation status to archived boolean.

Removes unnecessary complexity (status is only archived or not) and
simplifies model.
Show new message for at bottom of conversation stream.
Clean up SCSS imports.
Add in Bootstrap Javascript.
Kill BetaInvites routes.
Start splitting out account settings from user settings.

This commit looks like it has removed a lot of functionality and it
has. However:

* There was nothing actually on the financial page.
* Having separate controllers for each settings page is not very DRY.
* All the routing is setup better now.
Remove checkbox from conversation list.

Feature isn’t implemented yet, so it’s just confusing in the time being.
Kill some dead HTML/CSS.
Removed the columnar nav.

It was more trouble than it was worth. We may move back to it
eventually, but to implement it correctly takes more work and distracts
from core selling features.
Extract ApiController.
Serializers for Messages, People and Conversations.
Remove dead code.
WebhooksController base class.
Update Serializers.

Using a BaseSerializer cleans up a lot of the serializer code.
Include root in Serializers.

Thanks @vanstee for pointing out the security venerability in exposing
root level arrays in JSON.
Restrict => Authorize (more positive)
Overhaul of API methods.

They work! They need Auth! It’s actually usable!
Overhaul Mailgun controller.

There was bugs with creating attachments, creating new messages etc.
Now with more intelligent retries, more robust creating and clear hooks
for integrating with the API.