Mafia: Theme variables

This will parse variable:(name) strings in theme properties (this means **anything** can be a string now, with the exception of the 'variables' global theme property). **This doesn't add new gameplay features, it only simplifies certain themes massively (by making code reusable easily)**.

It will only affect themes that have a 'variables' global, old themes are untouched.

@IceKirby I had to copy some of the code to the theme checker for it to accept the theme, you'll probably want to change it.

Test theme used: http://pastebin.com/raw.php?i=buWYXTUq 

I'll make a post on the how to make themes thread later (once this is accepted of course) with a better example theme.