New LUA Functions: SetServerVariable and GetServerVariable

[Jabantiz]

These functions should only be used when you need a server wide variable and it needs to persist through server restarts.

GetServerVariable()
SetServerVariable()

These are used to manipulate the server variables stored in the `variables` table in the DB. To make it easier to identify variables added through lua the server core will add "lua_" to the front of whatever name is provided.