Suggestion: Full cover preview at search results (was write access to "CurrentPreview" from within ParserScriptAlbum)

[Florian]

@Florian

2. A way to modify CurrentPreview from ParserScriptAlbum so that you can use %_preview in creative ways^TM and restore its actual purpose in ParserScriptAlbum.

3. A new technical placeholder similar to %_coverurl% for ParserScriptIndex that is filled with the URL of the actual cover image that's used when importing the release. This also would allow for a Cover button to be added next to the Preview button.

I've added those two with Mp3tag 3.36-beta.6. The new placeholder is named %_coverfullurl% and I already updated the builtin Tag Sources accordingly.