Email integration

Not ready for pull yet, and destined for 4.9, but worthwhile opening for discussion.

```
Necessary setup: configure your mail server so that it automatically bcc's an "archive"
email address. Put the creds for that address in the config file.

Not sure if this is possible with gmail, I think it's unlikely:
http://thenextweb.com/google/2012/07/03/if-youre-a-google-apps-admin-you-will-now-have-access-to-a-gmail-log-search

Gmail has lots of nice integration options, and this route could easily be expanded to
use the gmail API without changing its own API to the xTuple clients.
```

This code exposes a REST endpoint to show all messages to/from a particular email address. The way the Qt client would consume this endpoint would be that there'd be an email tab in the contact workspace (something similar could be set up for accounts, too) that would make a HTTP request to this endpoint, and would render the resultant JSON however it sees fit.