Start/End timers when adding music to the library.

[pironic]

reliant on issue #17 - bonsai library.

know all those tracks out there on youtube that are full album mixes? we could utilize those by keeping track of track length and starting time on a song. that would also eliminate problems with intros or outros on a song

when a user is adding a song to the library, we default to start of 0:00 but they ca override, they can also input song ends at time.