queue player plays from, playlist populates queue only

[dxstiny]

allows shuffling & dynamic precaching #13

[dxstiny]

allow adding any song to queue

• play next
• play last

[dxstiny]

yet it shouldn't just copy from the playlist to a new list; it should update if a new song is added to the current playlist

so a "parallactic" list might make sense: a class inheriting from list (that secretly stores two lists, instead of one) overriding "append" to append to both lists.
meaning that one list can destructively be shuffled & sliced without actually modifying the real playlist, and having the possibility to revert to the original playlist & order