Re-add folders for the general library appearance

Based on App Store reviews, users adored the folders and don't see playlists as an adequate replacement as it does not clean and organize the library screen.

See also: #671 (closed).

changed milestone to %Future

added Feature MediaLibrary Regression + 1 deleted label

changed milestone to %3.2.2

This should be implemented as labels with the new media library.

Especially the previous drag and drop implementation by @caro is referenced as very popular and people loudly complain that it is gone.

changed milestone to %3.2.3

changed milestone to %3.2.4

changed milestone to %3.2.5

changed milestone to %3.2.6

changed milestone to %3.2.7

changed milestone to %3.2.8

This was addressed by !154 (merged)

closed

assigned to @bubu