Hints for muse in main

Warnings

• asv-tag-empty
  org.musesequencer.Muse3.appdata.xml:9 - translation
  The mentioned tag is empty, which is highly likely not intended as it should have content.
• asv-type-property-required
  org.musesequencer.Muse3.appdata.xml:9 - translation ()
  This tag requires a type property.
• screenshot-save-error
  Unable to store screenshot for 'https://muse-sequencer.github.io/img/arranger_new.png': Can not store source screenshot: Fatal error reading PNG image file: bad adaptive filter value