Update a download manager testcase
Update test case and documentation for local DB methods

These are not guaranteed to return references to the same object on
repeated calls.
Remove the global DB lock

The DatabaseHelper is synchronized itself, therefore we can get by by
using only a single instance of it. Since we are now using the same
database connection all over the application, we only close it when
MainActivity is destroyed.
Remove noisy debug output
Update the TODO file
Pause playback on PHONE_STATE and HEADSET_PLUG

This receiver is responsible for pausing playback if a headset is
unplugged or a call is started.