This commit improves the use of mail activities by allowing their
integration with the calendar. Activity types now have a category
field that can be used to trigger some specific behavior. First
specific behavior is to have activity types of meeting category.
Creating activities of this type trigger a jump to the calendar to
schedule the meeting. Meeting activities and calender events are
linked to be able to easily navigate through the document, its activities
and its meetings.
Configuration is done using a category on activity types instead of some
hardcoded "meeting" activity to avoid issues with master data and to be
able to choose which activity type should trigger this behavior.
Akash Bhavsar
9568b1525b