Hotwiring

Adds security system part to most vehicles that would believably have one. Vehicles with a security system have a chance of spawning with no keys (locked controls). A new flag for vehicle parts was added "DIFFICULTY_REMOVE" which requires the same difficulty to remove as to install.

Player can hotwire the vehicle which involves a mechanics check. If this fails, alarm will start, which makes loud noises. There is a chance the controls will unlock anyway. If the player tries to hotwire and the alarm is already on, the controls will always unlock, but the alarm will not turn off. 

When the alarm is on, and the controls are unlocked player can interact with controls as usual with '^' and an extra option to 'Try to disable alarm' when the vehicle isn't moving. This can damage the controls and the alarm part. When the alarm part is destroyed, the alarm stops. 

Alarm has a chance of stopping at any time, and stops when the battery is dead.

Mechanics 7 and above essentially guarantees success at hotwiring. Alarm can manually be triggered with a screwdriver, or by activating the controls when the vehicle is unlocked.

~~This PR essentially adds a useless Security System part to vehicles, so I was thinking that the player could 'Trigger alarm' to make it attract zombies and have some kind of use, aside from just annoying the player.~~

~~Cars may spawn without keys in ignition, requiring some kind of bypass in order to use them. Similar to #421, except I won't be adding/spawning keys. Assumed that vanilla behaviour implies keys are already in the ignition.
Critical failure will mean that an alarm starts, alarms will last until batteries are flat, then will not come back on.~~