[IMP] mail: improve usability of activities

Purpose of the task is to improve the usability of activity types and
activity scheduling.

Another purpose is alto to protect some master data activity types by flagging
them and preventing their deletion.

Containing
 * make the activity type as master data so deletion will be prevented;
 * improve the usability of the activity type;
 * prevent the deletion of activity type which are used for automated activity;
 * change the usability of activity scheduling modal;

This commit is linked to task ID 1907970 and PR #29257.