- move network connection handling out of Job into Session

- move job scheduling out of JobQueue into Session
- jobs use the thread-global default session if no session is specified
- auto-reconnect if connection to server has been lost
- support arbitrary session identifiers (needed to solve indirect notification loops)
- make Job a KCompositeJob, allowing to easily execute sequential sub-jobs
- since Job derives from KJob now, jobs are auto-deleted after execution

svn path=/trunk/KDE/kdepim/akonadi/libakonadi/; revision=632537