Visual overhaul and another way of inserting a section. The section code 
is saved to a global variable which can be used as well. Does obviously 
not work accress edit sessions or different units, therefore the old way 
is preserved.

- Remove global dialog style

- remove ID handling from model classes. This is now done by the editor 
itself (mainly unit service).
- Rename and move IDManager to editor as IDService

Now properly finds all normal and simple drop lists.
This is achieved by a new method of unit all it's sub-components, which 
returns all contained elements with and optional type filter.

Also improve (still not very pretty) styling of the drop list props 
panel.

#260 #259

Add 2 new menu buttons to the section menu.
One simply copies the selected section to the clipboard.
The other opens a dialog where a copied section can be pasted. The 
section element's IDs are checked if they are available and a warning is 
shown.