Implement a cover index

[The4thLaw]

Description

Demyo 1 had an index page where you browsed the library through the covers of the albums.

Demyo 2 should have the same. A default image should be shown if the cover is missing.

Perhaps this should be handled from a button managing the presentation in the menu bar (like in Google Drive), stored in the configuration and used for all Album indexes (favourites, reading list...).

[The4thLaw]

Moving to 2.3.0 to avoid feature creep in the Vue release.