SyncJournal: Fix logging text.
SyncEngine: End the journal transaction after update.
FolderMan: Proper singleton implementation.

The connect in SocketAPI had to be moved because it also uses
FolderMan::instance(). And since SocketAPI is instanciated in
FolderMans constructor, this was a deadlock.

Now the connect is tried on every new socket connection in SocketAPI
but I assume that multiple attempts to connect are not an issue.