Don't send update failure notifications for certain folders

Seems that some Android 7 devices insist in update contacts also in read-only folders.
This leads to several notification mails for the users (while the user is not actively doing anything with these contacts).

We could introduce a static "don't send notifications for these folders" list in the kopano config.
It would also be possible to have this as additional flag in the Shared-Folder-API so the user can disable these notifications as well.

Request in forum: https://forum.kopano.io/topic/307/problem-mit-p9-lite-android-7-default-mail-app-and-z-push/7

Also update https://wiki.z-hub.io/display/ZP/Sharing+folders+and+Read-only and https://wiki.z-hub.io/display/ZP/Tools%3A+z-push-admin to match the changes.