Add animation when toggling between months

[adam-knights]

Within the material design spec, rather than changing from month to month in a 'harsh' way as we do currently, instead move the month out left/right or right/left and the new month in.

See the video halfway down https://material.google.com/components/pickers.html#pickers-date-pickers for a demo of how it should look. An implementation of the animation can be found here: http://www.material-ui.com/#/components/date-picker.

Rather than add liquid fire as a dependency we may want to consider doing this ourselves with clever use of variables, the Ember run loop and afterRender.