This avoids problem with the selected index when moving pages.

#737

Not closing the menu does not make sense when moving or deleting pages.
It was only useful to avoid closing when clicking on the menu without 
clicking a control. Losing this is acceptable.

Also disallow deletion of only non-permanent page.

#736

It now uses the page index the menu (that was used to delete) belongs 
to, instead of the selected page index.

It now always uses the old mode.

Also refactor a lot of stuff around the page canvas and unit view.

#684

#681

#686

New section components no longer get their number on creation. This has 
the effect that the section gets a new number and is updated again with 
all others after that.
Numbering of all sections is triggered in one place (UnitService) and 
updates all existing sections.

Everybody is considered expert but role 'developer'. The host 
application allows not saving the unit when rights are insufficient, so 
the editor needs not to take care of that. Having full rights allows for 
better inspection of units even if it can't be changed(saved).

This fixes Tables which houses elements without dimensions.

Now always use grabbing when dragging.

This feature is incomplete. Button is hidden until it's done.