Create a shared instance of SAMHUDView and more…

Adds the ability to create a shared instance of SAMHUDView. So, now you could just do `[[SAMHUDView sharedHUD] showWithTitle:@"Loading…"];` and not worry about allocating an instance, and it'll work fine across view controllers and stuff.

Also fixes some deprecated methods in projects compiled only for iOS 7 and above, while still maintaining backwards compatibility for older SDKs.

I should go to sleep now. Goodnight...or good morning...whatever.