Add Windows Command Prompt Template

New `windows-command-prompt` template. This builds a `reg` file for importing to the current user's default command prompt settings (If a user has customised the settings of a particular shortcut or program, these are not inherited - they'll need to be deleted from the registry manually).

This required adding a `to_hex_bgr` method for switching around the hex value to suit the way Microsoft store their colours in the registry.