Dialer object and associated tests

This pull request gets test_dialer and test_call_log in shape, but neither are passing yet:

1. The dialer app suffers from the double-click problem with tap https://bugzilla.mozilla.org/show_bug.cgi?id=829566, but once that is fixed the tests should pass.

2. The test_call_log_missed_calls test won't pass until we add a step to make a call to the phone.