Changelog ver 1.107, 2016 09 06

* stable driving, no more jumpy tractors
* it should be much more difficult to roll the tractor over (ony in extreme tight driving on uneven terrain).
* wheels on front axle shouldn't go up even in tight corners
* adjusted accelerations
* a bit lowered vehicle sale prices, should be no more earning by buying/selling used vehicles
* no door sound on entering/exiting doorless machine
* engine sound doesn't get quiet when driving cabinless vehicle
* brakes switchable in game menu - between hard as they were and softer.
* added Invert Y axis in game menu - works for mouse and analog controllers.
* idle tractor engine sound after exiting tractor with engine on
* Kuhn Sitera 3000 cultivates as well during seeding - no additional cultivator pass required
* wheels get dirty in similar same rate as vehicle chassis do (actually a bit faster)
* wheels get clean over time while driving on wet (chassis does not)
* wheels get shiny and wet while driving on wet
* dirty and worn states get properly propagated over wehicle parts
* time to get completely dirty effectively shortened to 1 hr (real time)
* properly saved and loaded type of tractor wheels
* improved parameters of overfilled trailers
* fixes for grass and terrain inside animal buildings