Beta Hybrid Citybus 8.1.0

I've made lots of improvements to the handling and performance of the hybrid system and fixed several bugs/nuances found by community members. This update to the Citybus is accompanied by the same updates to the ETK800 Hybrid!

Improvements to Citybus:
- Engine idle stop is now enabled by default on the standard configuration (and can be turned off in the Tuning tab). Unlike the ETK, the bus engine will only shut off if the brakes are held beyond a certain point and the speed is below 15 MPH, which avoids excessive stopping and restarting of the engine when driving at low speeds.
- The bus now features an ambient "air conditioning"/"air compressor" sound courtesy of freesound.org so that the game isn't so eerily quiet when the engine quits.

Bugs fixed:
- Now works properly with cruise control app
- Vehicles with things such as daytime running lights (anything dependent on electrics.values.running) now work correctly even when the engine is off.
- Driving in reverse now drains battery instead of charging it
- Improve smoothness of engine starting/engaging while the vehicle is moving (overrev is far less likely)
- Vehicles are now more powerful when battery is extremely low (but the battery doesn't charge up as fast at high throttle)
- Regenerative brakes are more stable