[Feature] AppImage Version Detection and Handling Multiples.

As per #10, this is the proposed way for detecting .AppImage versions. Putting this here so we can gather feedback on it. The current implementation currently matches for files with the .AppImage suffix.

> So thinking about it again maybe we could do something much simpler which would cover at least >80% of cases:
> 1. Look for files with the .AppImage suffix
> 2. If there are at least 2 - characters in the filename, remove everything behind the second-last - character from the filename
> 3. there is only one - character in the filename, remove everything behind the -
> 4. Replace _ with
> 5. Compare the result against what the user wants to launch to determine whether we have a candidate
> 6. If there are at least 2 - characters in the filename, assume that what is between the first and second - is the version; this will be needed to decide amongst several candidates (to pick the latest version)