Add the ability to modify tags

[jverkoey]

In the UI, this would ideally be represented more abstractly as "tags". When exporting the library, you could choose to export the tags to a specific field (e.g. grouping) for the purposes of use in Rekordbox.

[jverkoey]

I've started adding this functionality using a SwiftUI form editor. The entry point looks like this:

which pushes an interface like this onto the side pane's navigation controller:

[jverkoey]

All of this is currently ephemeral and needs to be wired up to the database in some form. Still considering whether to make changes instantly or to implement some form of an editing mode with a Cancel/Done button.