Broken fixed-layout FXL page transition effects

[danielweck]

Looks like the combined CSS presentation effects on iframe contents and iframe parents do not work anymore, probably something to do with animation timing (easy to check with setTimeout() on the END transform), and the "scaler" container for the page (zoom applied to the HTML element of content documents vs. the iframe's div parent). Disabled feature: https://github.com/readium/readium-shared-js/commit/4bfb03996e9a641084d833df5bee4dc95343a99c https://github.com/readium/readium-js-viewer/commit/d16545b0b621bcd7e6186cf9ee6b175894e3bba3

[rkwright]

Leaving this open to track the fact that the transitions are disabled.