- Swap the position of dialog buttons

- Add translations for operators
- Improve and extend the evaluation of visibility rules

This hack allows the page tabs to have a pseudo tab to create a new 
page.
This tab is disabled so the user can not change to it, but is still 
clickable.

They are treated as containers by the player and therefore have no
values that can be queried.

- Fix typo in css classname

- Basic implementation

Also restructure files containing interfaces.

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

- Background color must not be transparent for the stickied panel to 
overlay properly.

- Use TextImagePanel where possible

Toolbar is a single word, therefore any capitalized letters are errors. 
No need to sanitize, since this was broken anyway.

#384

#386

... instead if setting the value directly on the object. This way 
elements can react to ID changes. This is necessary for DropLists since 
a changed ID has to be reflected to child elements.

#445

Less unneeded scrollbars and fixed height.

Th actual clickable area is displaced by that, which is hard to fix. So 
the worse layout is accepted for now.