Add editableVehicles preference

[carsakiller]

Adds a new preference editableVehicles that defaults to true, meaning player vehicles are, by default, true. If toggled off in the addon config menu or using ?setPref, any newly spawned player vehicles should be uneditable.

So far, this is completely untested, just opening to show some life. Will need to make sure that when the world is reloaded, previously uneditable vehicles are still uneditable. If they somehow are not, we will need to save a editable state to G_Vehicles for each vehicle so that onCreate we can set the edit states of all the vehicles.

Things to test:

• Vehicles are editable by default
• Server vehicles are unaffected
• When editableVehicles is set to false, new vehicles cannot be edited
• When editableVehicles is set to false, server vehicles are still unaffected
• When editableVehicles is set back to true, new vehicles can be edited
• When editableVehicles is set back to true, old vehicles cannot be edited
• On reload, vehicles that were spawned as uneditable are still unable to be edited

Closes #95

[Sedrowow]

I could test this as soon is i got home (about 14:30 UTC+1 (i am in Germany))

So if ok, i try the required test according to your writings as soon as i am online.