Honour the online/offline setting requested by a client application in every case.

Previously it could happen that the resources were set to offline mode, but due to an event,
like resume from suspend, or network reconnect, the resource went online.
This had bad side-effects, like downloading mails while KMail was in offline mode.

Yes, it is a bug, that was there even in KMail1 times. :)
I CC to other bugs about offline mode, although I'm not confident it fixes those problems.
Feel free to report success/failure for those cases.

FIXED-IN: 4.9.4
BUG: 195300
CCBUG: 300086
CCBUG: 298956
(cherry picked from commit 75a744dd)

Conflicts:
	akonadi/agentbase.cpp