Store contacts that the user had a conversation with in indexedDb from the worker, and show offline contacts in the sidebar.
Silence the 'ContraintError' message logged to the console when adding an existing contact.
Merge remote-tracking branch 'upstream/master' into indexeddb
Add a test for the storeContact function.
Address most review comments.
Add a unit test for the code merging the local contacts with the online contacts received from the server.
Merge pull request #140 from fqueze/indexeddb

Store contacts used in previous calls, and display offline contacts in the sidebar.