Power supply enhancements

I would like to add the Master Key, the key that activates the systems of the cabin, and the battery switch.

I will not implement it as a script. I will just implement two modes that can be activated by an ENG file parameter :
- always activated (default behaviour in order to keep compatibility)
- manually activated by driver
This will be used not only for TCS but also for the braking system, activating the screens, etc.
So, I will also add a cabview control and a keyboard assignment.

Other possibilities :
- Add conditions for cabview controls (for example : shown only when battery is on, shown only when master key is on)