Build correct share plugin version
With this, I believe the plugin support is finally fully in place!
- Make sure $TARGET_VERSION (e.g. "4.4.0.58") exists when building in sfdk
- Use the two first numbers of the version (e.g. "4.4") to determine the version in comparison-friendly way
- Build v1, v2, or no plugin based on the
--with shareplugin_v[1|2]
- Check that Sailfish OS target version matches the (possible) share plugin version
- Don't allow both flags at the same time
- Enable one or the other flag in CI