Formatting mainly

Indentation should use 4 spaces consistently. No need to return without anything, a function returns without with None (same behavior).

Did not change some odd things I notices, like property registration inside of operators - this should only be done in `register()`, or a function that is called from there. 

Not sure about the use of globals, and if it's reliable to get paths via `bpy.utils` in global scope (is executed on load of the file). To avoid the "global" keyword, you can also use a class with static members:

    class G:
        global_var1 = "foobar"

    print(G.global_var1)

What is the purpose of `@persistent` if you don't use it for an app handler callback? (`load_settings()` it called directly in `register()`).