Add classic left-click orders

This is based on the HotkeyAddon branch by @TiriliPiitPiit (reversed commit 9a655d1a46fc631b5fe27074acdab00c2d6e1717 and http://dpaste.com/874285/) with some changes:
- Simplified the case whether to do action or select. It is a little annoying to use as you have to deselect all units to select new units, but it does not break so easily. This fixes the issue when you attack click and select the enemy unit loosing focus of your army. However this could be tweaked to behave more like C&C.
- also added the setting to the CnC mod settings GUI
- AttackMove also works with left-click. Looks WorldCommandWidget.cs was simply forgotten.