Add app/project name to uservoice

# Problem

Need to be able to route tickets to queues based on the app that generated the issue.

# Solution

There are three things in here, and any one of them is probably fine:
* project name in subject
* project name in message
* project name in `app` custom field

I have no idea how to execute or test this, so hopefully someone can let me know if this is right
The user must configure custom fields server-side, so I think the idea here is that bugsnag can send its own custom field which is ignored by default.  The user can then add it to their UserVoice and route based on it.  The name I chose a) clearly indicates where it's from and b) maps the nomenclature Bugsnag uses.