Pan animation after adding a new page isn't smooth

This issue has been migrated from mozilla/webmaker-android#1947.

It was originally written by [flukeout](https://api.github.com/users/flukeout) on Wed May 20 2015 and had the following description:

> When adding a new page that would expand the bounds of a project (very left or right for example) the animation that brings the page into view after adding it is jerky.
