Update Keyboard.org
Restore lost contents in Documentation/Developer/Keyboard.org
Cleanup in documentation
Merge Shortcuts.org and Keyboard.org. Refresh and cleanup contents (not finished yet).
clang and llvm RPMs were added to the Packages
Mouse Preferences: implement setting mouse speed; apply saved setting at Preferences startup.
Added new developer doc file Keyboard.org. This is the place to document keyboard usage notes.
Update README.md