Harsh switch in tab to tab_group transition

[Matt Layman]

There is currently a nice smooth transition between tabs when switching in horizontal motions (e.g., artists to albums in the music screen). However, that same type of smooth transition does not occur between an active tab and the tab group (e.g. moving up on an album back to the artists-albums-playlist tab_group).

A smooth transition would probably add a surprising amount of polish to a UI element that is so common in the project's interface.