Beta Hybrid Citybus 8.1.0

This update includes a complete rewrite of the hybrid system! (Okay, some of the code is just moved around, but still)

I took the time to properly organize a lot of code that was sort of tossed together in my initial versions of the hybrid system, and made it much easier to maintain and read. I also spent a lot of time researching hybrid gearboxes and doing a ton of algebra to perfect the equations and simulation logic the mod uses to simulate a hybrid powertrain, and the results are that the BeamNG hybrid powertrain is much more refined and feels way more natural. The efficiency and performance are both greatly improved, and the throttle/brake feel is much better than it used to be.

In addition, the following notable changes have been made:

• The "City (Hybrid)" variant of the bus now has its own skin with the infamous "Clean Air Hybrid Bus" wording along the top
• There is now a "Zebra (Hybrid)" variant for those fuel-efficient treks through Jungle Rock Island
• Fancy new startup sound for the bus as the hybrid system initializes (hey, beeping is fancy!)
• Bus defaults to being powered off when it spawns. Hit "V" to power up the hybrid system. (this can be changed in the tuning window)
• "Fast Charge" mode has been removed. A new "Charge Hold" mode has been added, which can be engaged with the same keyboard shortcut (Shift+E) at any time (not just in Park) and will attempt to charge the battery even while driving.
• Refined powertrain device tree. eCVT now has its own built-in torque limiting clutch, so no separate clutch device is required.
• Thumbnails for all variants! Finally! Truly living in the 21st century here.