- Fix element creation to have new value objects instead of referencing 
the old one
- Add new IDs to DropList value objects

Options are now possibly rich text. This needs to be taken care of.
Also use extra span tag to preserve all whitesoaces in the index-suffix.

#279

Top and bottom were mixed up.

#291

- overflow of lists is now hidden to prevent dropable elements from
being displayed outside the container
- placeholders are hidden with flex orientation

 - Remove duplicate code in keypad templates
 - Extend the use of the configuration file

- delete french keypad

- add translations

Use a horizontal aligned placeholder for dynamic aligned drop lists
when there is more than one element in the list

- Refactor variable of the placeholder dimensions

- Important for vertically positioned drop lists
- Analogous to the calculation of the height

- Replace pixel calculation with percentage values
- Use of only two modes: full fill or line

#291

#343

#294

Red background looks really bad, so we just adjust the border color.

- 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

Just called from the editor, before creating the Unit instance.
It goes through all IDs and checks for duplicates. If found it generates 
a new one and shows the prompt.