Add custom page view implementation

[rechsteiner]

We're currently using EMPageViewController as a replacement for UIPageViewController, as it’s more predictable and provides us with much better delegate methods at every step.

Ideally, we would replace this library with our own custom implementation to have even more fined grained control. This would also fix an issue with EMPageViewController where it occasionally won’t do anything when swiping rapidly between many pages (#26).

[rechsteiner]

This has been implemented now (#468) and will be part of the 3.0 release