KolabMailAccess: added comment about server sync when switching from online to offline
KolabMailAccess: added comment about server sync when switching from online to offline

* we disconnect from the server (go offline) without
  implicit sync
* sync function needs to be called separately (not yet
  sure exactly where to call it, as long as we do not
  have a dedicated backend synchronize() function which
  gets triggered by some EClient action)

GNOME/evolution-kolab,GNOME/evolution-kolab