Cleaned message form params

These values were ignored by strong_params and were outputting warnings
to the log.
Add internal messages

This allows a user to mark a message as "internal" so it's only
available to agents.

Added here are:

* The migration for the 'internal' column
* A slider switch for choosing whom the message goes to on the form
* Proper user selection for e-mails based on 'internal'
* Display internal messages with a highlighted background.

No designs or styling for these elements has been conceived or presented
yet, so I used the most basic functional styles possible.
Show proper URL for example POST

Just sliding this in, it helps in dev to generate a message and just
copy/paste
A ConversationStream object for displaying conversations.

As discussed in #158. This also solves #167 too.
Notes model.
Split out colors from logical colors.

Great suggestion from @chexee.
Default avatars

Creates the concept of the “default sized” avatar. Includes new helpers
and a more flexible base avatar helper.
Shows notes in the conversaiton stream

It’s pretty good so far, however creating notes is still broken (or
just uses the internal property).