Proper implementation of async

Aslo removed the option to use async downloading as this is now default.
Re-factored, fixed init error
Removed 'Download' method

This is now in Wallbase.cs
Formatting
Re-factored and fixed several bugs

- Corrected the order of checking if url and path is valid or not.
- Fixed settings bug where it didn't save it's state
Added 'Remember URL' option
Fixed 'cancel' bug
Properly implemented cancel method
Removed 'Use async' option

- Removed 'Use async' as this is now default
- Added 'OK' button
Fixed settings, now saves properly
Added saveUrl option
Bug fixing