2 commits: Floating search button animation & [Fix] AppDetails: Card covered inside header graphic

Hi guys 😚

I can't split the 2 commits (Git not happy) because I didn't create branches, it was my mistake I think.

The 2 commits are:

• Floating Search Button animation (shaking) Ref: https://gitlab.com/fdroid/fdroidclient/issues/868
  A simple shaking Search button, you can adapt at your convenience.
  I adapted the code to avoid multiple user clicks on the button and several opening of app list.
  Works great :)

• There is no more overlap and better for users. Ref: https://gitlab.com/fdroid/fdroidclient/issues/1030
  We can do more with coordinatorLayout, I will study the subject lol.
  (v) Tested in all themes
  (v) Portrait/landscape orientation
  (v) Call from 1st tab and Categories