[#3028] Generate safe track event with end.
[t3041] First pass at media editor for sequencer + gallery
[t3014] Added media stuff
[t3041] Slight spacing issue and FF overflow issue fixed
[t3041] Added test check into mediatypes.js
[t3041] Update source directly after updating start and end so that the source works
[t3041] Use popcornOptions to update
[t3041] New sequencer update in media editor