Scan for changed metadata id3 tags

[Daniel Schürmann]

Once a track is included in Mixxx, the metatdata in library is treaded a s the master. This prevents slick interaction with external tag editors.

Idea: Lets introduce a "changed from Mixxx" or "form taglib" flag, to distinguish if it is the pure metadata from the file or manually edited in Mixxx,

This way, we can automatic re-load the metada during the scan process. if the files mtime has changed.

[Daniel Schürmann (daschuer)]

Related: Bug #1204164

[Uwe Klotz (uklotzde-deactivatedaccount)]

As a workaround the following PR adds a new library option for implicitly reloading tags from files whenever the corresponding track is selected/loaded/edited:
https://github.com/mixxxdj/mixxx/pull/592

Use with care and make backup of your Mixxx library first! Enabling this option in the library preferences dialog will also display a warning message.

[Uwe Klotz (uklotzde-deactivatedaccount)]

The PR mentioned in the previous comment has been replaced:
https://github.com/mixxxdj/mixxx/pull/728

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/7377