Better Docks management

MainWindow adds dock at previous position
Dock wan't be shown on restoreState, if not added to main window
Open multiply REPLs
Python REPL
Fix: Start the Enki binary without a console.
Docs: Update pyinstaller directions: have user install it instead of running it from some path.
Fix: Include missing colorbutton import.
Docs: Word-wrap lines to 60 chars.
      Update license to GPLv2 instead of v3.
Tests: better fail, if ctags is missing
Tests: better output, if markdown or docutils is missing
Avoid crash in UISettings on termination
Tests: Fix error message if module is missing
Fix: Restore missing cd so installer builds.
Docs: Specify path needed for ctags.