transport-xmpp: Cleanup of Exception handling

aSmack 0.9 introduced a few changes to the Exceptions thrown by the
API. The result is cleaner code and less try/catch blocks. We now
adopt the new style and remove some now obsolete comments.
transport-xmpp: Fix reconnecting 'deadlock'

XMPPService could get into a state where it continuesly tries to
reconnect while simulatenously blocking the main thread. But this also
prevents SmackAndroid from receiving ConnectivityChange notifications
and calling Resolver.refresh() which leads to unuseable DNS server
information. Therefore every connection attempt failes because Smack
is unable to resolve the domain. The reconnect loop starts again,
usually because there is another intent like SET_STATUS in the queue,
and the main thread is still blocked.
transport-xmpp: Make nested 'State' enum static

although they are implicitly static (as per JLP 8.9) it's better to
declare them excplitly as static.
transport-xmpp: Changed aSmack version to 0.9.0-SNAPSHOT-2014-04-01