Move Akonadi serializer plugins to respective repos

* addressee and contactgroup serializers to akonadi-contacts
* kcalcore serializer to akonadi-calendar
* mail serializer to akonadi-mime
* kalarm serializer to kalarmcal

By having those serializer plugins in those repositories it is possible
for Akonadi to be useful to third-party applications without having to
depend on kdepim-runtime, which may not provide anything useful to them
(except for the serializers) and it's also more in line with the
Frameworks-like structure.