adding first unit test for search of address book provider
Move creation of default address book to backend
Fixes owncloud/contacts#513
Fix creation of default address book
Add MySQL to travis run list to make sure unit tests are working
Should fix not installed error
Fix typos
Also test deleting of child
Fix mistake
Connect pre_deleteContact when unit tests are run
only purge not deleted contacts
Undo wrong change
getPreferedValue returns value with PREF flag
Fix Addressbook::childExists($id).

Return false instead of throwing an exception if there's no child with $id.
Also, add a test for that function.
Fix log output in purgeIndexes().
Add displayName() to GroupController.
Prepare for sharing of contact groups.
Delete groups by their id instead of their name.
Rename group by id.
Fix and re-activate Contact sharing backend.

While not needed for actual contacts sharing (which is solely done via
the Addressbook sharing backend), we need its isValidSource() function
in core's \OC\Tags::getIdsForTag() (which implements \OCP\ITags::getIdsForTag()).
It is required there to test if the items that are tagged with a given
tag are actually allowed to be accessed by the user, i.e. owned by the
user or someone who is sharing it with the user.
Include shared groups.

Fixes #38.