Add --version option + update docs / issue templates

[theblackhole]

https://github.com/TheAssassin/AppImageLauncher/issues/338#issuecomment-729734197

Currently, the only way to get AppImageLauncher version is to use AppImageLauncher --appimagelauncher-version which is not documented and non-standard.

Replacing (or aliasing) --appimagelauncher-version by --version and/or -V would make it easier to find. Also updating the doc and issue template with this info would help with issue diagnosis and help users staying up-to-date

[TheAssassin]

AppImageLauncher transparently forwards all arguments to the AppImage it executes, except for those prefixed with --appimagelauncher-. I'd rather keep that consistent.

For ail-cli, we already have that feature:

> ail-cli --version

It's only really missing for appimagelauncherd, and perhaps for the update/remove helpers.