Closese #2029
Added a basic conflict detection functionality to the Shortcut Mapper.
This includes:
* Marking conflicts with a different background color.
* Displaying conflict information.
* Warning when attempting to assign an already existing short-key.
Some more related changes to the Shortcut Mapper:
* Fixed some bugs, for instance:
1. Babygrid was shrinking on any attempt to adjust its position to integral
rows.
2. Context menu entries were enabled for empty lists. Using them would crash
Npp.
3. ... some more minor bug fixes.
* Performance enhancements to Babygrid.
* Minor UI improvements.
* Babygrid is configured dpi aware.
Close#1229, Fixes#385
Only build errors are fixed, compile warnings are left alone. To reduce
the number of changes, even the compiler option "-fpermissive" has been
used to downgrade several errors to warnings.
