Add tests to verify behaviour of a basic chatroom with CPIM and IMDN

enabled

Make more robust database migration code as the user may set database
paths but instruct the core not to initialize the database. This
behaviour can de achieved by the following lines in the rc file:
[misc]
use_database=1

[storage]
uri=null

By not explicitely disabling friends, call log and chat database, the
SDK assumes that they are enabled and migration sould be carried out