Make search-bar scroll out of view on the Explore tab

[AmionSky]

On the Explore tab search bar takes up quite a bit of vertical space and is unused if just looking through the discover posts.
Would be nice if it would scroll out of view.

Example of what I mean:

scrollaway.mp4

code: https://github.com/AmionSky/mastodon-android/tree/scrollaway