Bugfix: Make the quit shortcut global.

The quit shortcut now works even in editors.
BugFix: Enter/Backspace handling when at start of line.
BugFix: Open Watched files in editor if configuration says so.
BugFix: When closing a modified tab, give the user the choice to save/cancel/close

  -- previously, the user either had to save or cancel,
     now he is presented with a message box
Feature: Start of a simle search & replace widget.

Currently only the search functionality is implemented.
Feature: Implement search in the editor.
Documentation: Cleanup + one new line.