Dispatch cleanup

[RocketMan]

This PR refactors the top-level actions addTrack and moveTrack to stemmed actions under editList; namely, editListAddTrack and editListMoveTrack, respectively.

In this way, we lose the overhead of extra routing at the top level and instead delegate it to Playlist.

This is a non-semantic change.

[RocketMan]

Closing, as ideally, both of these operations would move to the JSON:API.

For that to happen, we'll need to address a couple things:

• addTrack contains a UI fragment in its response that our JSON:API equivalent does not provide. We'll want to do that in a way that is reasonable for both the API and the application architecture;
• moveTrack performs track resequencing, and while there are several examples of similar operations in REST APIs (See Spotify and Google), there is no definitive, best practice to guide us.