Add saving of compression method choice

[SnoutBaron]

Allow the user-selected compression method to be saved so that when the tool is opened, in future, the last selected compression method is read and applied.

Since the program already writes to the registry. I would suggest creating a simple subkey with just a number ranging 0-3 that is set when the user selects a compression method and is read when the application begins.

[Iridium-IO]

This won't require writing to the registry, as there are inbuilt settings variables in the program that can be used :)