Bug 982663: collect and report app usage data

This patch does not have tests yet, and is still missing a couple of features, but it has working code and is ready for feedback and preliminary review.
We really should be making use of the ping URL called out in the makefile, rather than hardcode it here.

https://github.com/mozilla-b2g/gaia/blob/master/Makefile#L133

For QA testing - it would make my life easier if I had one spot to modify, since I usually use a mock HTTP server to do any type of ping testing.