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.

#736

It now always uses the old mode.

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

#684

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

Only works for a few commands (mainly page and section stuff).

- Adds new menu to page-bar, which shows issued change commands with a 
button to rollback the latest change.
- Added warning to the UI element that this is a experimental feature 
and can destroy units.
- Undo is done by having the normal function to apply the change to the 
unit-object and another to undo this change. The HistoryService manages 
the list and calling rollack (via UnitService).
- Further refactiring to the unit services.

- Encapsule into separate component
- No more pop-in-controls
- slicker ui layout
- More tooltip with explanations

#523
- Improve sanitizing of position margins

#511

- Add ReferenceManager to check if deleted elements are referenced 
anywhere in the unit. If so display a warning.
- Move page logic to UnitService

Remove 'any's be adding proper types and using 'never'.

Change translation key and meaning from 'typeAreaWidth' to
'sectionWidth'

Remove case distinction when labeling the page's margin width

The width of a page results from the value for the maximum width plus
twice the value for the spacing

- Now does unit (page) manipulation itself instead of delegating 
everything to the UnitService. Still need to call the UnitService to 
make it notify the API about the change to the unit.
- Also improve the hack for refreshing the tab view.

It did not do anyhting anyway. Is now integrated in unit view.

This is done according to the Angular best practices and minimizes
namespace collisions when using other packages which might use the same
selectors.

Technically the selectors are not even becessary since we use an Angular
component factory to create element components but it is still useful
for the DOM element naming, for debugging purposes for example.

Also focus the height input field upon opening the menu.
For the layout menu this does not work as checkboxes don't play nicely 
with menus.

In fact having anything but button in the menu is against the Material 
spec. But i still think this is the best way to achieve the usability we 
want.

Use unit field of UnitService directly to detect changes.

This structure moves closer to the structure template the team decided
on. Components and services are kept in dedicated folders instead of
following the logical code structure. This is still not the case here as
the unit-view component is still nested, but it's closer.