CPack: Add Inno Setup generator

Inno Setup is a free installer for Windows programs by Jordan Russell and Martijn Laan.

The new generator adds:

• A lot of options to customize the Inno Setup installer (e.g. custom installation rules)
• Start menu and desktop shortcuts
• Components (and also downloaded components)
• The generator is fully documented and tested by an appropriate unit test

Topic-rename: cpack-inno-setup