Added last checked-in venue, increased list size

Closes #18.
Increased venue list size to 20 nearby locations.
Erased test file
Updated the way venues are pushed
Updated appMessage code to be more reliable

Along with the UI tweaks for last checkin, I modified the appMessageQueue/Pebble.SendAppMessage code so that it doesn't fail as often. I also decreased the return list from 20 to 15, up from 10 in the current release. Closes #16.
Merge branch 'last-checkin' into dev