Split up library browser as separate, QCAD independent tool.

TODO

- Potential interaction with other products / release as separate product?

DONE

- Remove DB dependency from QCAD 3.
- start-up splash screen
- avoid drop in browser widget
- app name
- menu (exit, about, preferences)
- preference dialog
- fix app icon
- window title
- library browser as single app
- raise window to the top on start

Motivation

- Make QCAD 3 more reliable to start.
- Make QCAD 3 faster to start (if library browser not used).
- Reduce memory usage if library browser not open.

Interface with QCAD 3

- Launch Library browser from menu or tool button.

QCAD launches library browser for example as:
./QCAD -autostart scripts/Tools/LibraryBrowser/LibraryBrowser.js

- Insertion of library parts with drag and drop (like so far). No change should be required for this (?).