KolabMailSynchronizer: internal rework
KolabMailSynchronizer: internal rework

* moved code for updating an InfoDb record (including decision whether
  or not to set 'changed' flag) to own function
* this function to be reused in transaction preparation when in "take
  server" conflict solving mode
* renaming of summary variables to make clear they're of ImapClient
  origin

GNOME/evolution-kolab,GNOME/evolution-kolab