Make some class attributes private, add more interfaces to access attributes, change ambiguous variable names

[germanivanov0719]

• Car stats should be private (Vehicle())
• Change "img_x" in Car and Vehicle menus to normal unambiguous variable names

Assigned to germanivanov0719

[germanivanov0719]

No longer important after switching to pygame sprites, although some classes might still benefit

[germanivanov0719]

With the migration towards pygame stories, it is no longer applicable.