Migrate old settings to new locations

As per issue #622 again, also move the settings from the old locations to the new config file, then delete the old file/registry keys.

I basically added a version number to the config file which makes it easy to deal with incompatible changes in the settings between versions. Right now, there's only one migration case: if the config file contains no version, the old config locations are imported and then emptied. I did add behaviour to convert the older color scheme and digit grouping settings that were changed since 0.11 though. That's barely necessary, but I wanted to try it out.

I did test on Windows (portable and regular) and Linux; it should be fine on OSX, but I've no way to verify.