Added tests for SenderIdentitiesModel

In this commit, new tests for SenderIdentitiesModel have been
added. They test that items are in the correct places after inserts,
deletes, and moves. The tests also test to make sure that
PersistentModelIndexs work properly, and that the correct signals have
been emitted.
Merge remote-tracking branch 'amidon/master'
Update copyright details for Peter