Added additional checks and delegate callbacks

Added checks to prevent initializing one panGestureRecognizer every
time. Added methods to prevent selection if collectionView does not
allow selection. I found that clearing the selected index paths in
willEndDraggingCell sometimes would crash since it’s too soon, I
commented it out since it is done later. Added fix so that the gesture
actually is committed also if the pan is over the threshold value
Added velocity to validate whether deleting is OK

Added velocity parameter as well
Merge remote-tracking branch 'upstream/master'
Added bug fix for new behavior

Fixes horizontal orientation issue and acceleration to only trigger in
the right direction
Took out extra velocity check when a pan gesture has ended/cancelled/failed
update pod spec