Added Two More Demos

- CustomViewTransitions
    - Starting point for some killer transitions, edited-out lines are
necessary for sliding the two views left and right during transitions
(similar to pushing but with added spring recovery)
*Next Steps* - Add in feature to toss views aside, fold them up, and
crumple them then throw offscreen

- SwiftSideMenuDemo
    - Swipe from left-to-right and you have a blurred menu
*Next Steps* - Have main view transform back & (perhaps) to the right