minor fixes
incoming messages now have their own class subclassed from KonMessage
outgoing messages have their own class now, too
OutMessage class used now
enforced foreign keys in database
request blocking list according to XEP-0191 after login (not processed yet)
improved user list model
added blocking property to user model
improved roster listener
apply blocklist result to model. Concurrency problem arised.
added send blocking command methods
improved async connect. Unfortunately that doesn't solve the problem for blocking lists
block user buttons included in user list view (untested)