Undo revert of "Added experimental install button (#161)"

This reverts commit 71ad11ffedd234149ee7a3fa6aa62f0c37a8229a.
more gnome-ish image
Changed the icon-container's style (#161)
Added a proper 'install' button (#161)
Added style for 'Update' icon (#161)
Cleanups.
Added icon for ColorZilla.
Revert commit
Revert again.
Remove useless png
Merge branch 'master' into download-experiments

Conflicts:
  images/icons.svg

(Re-added eyedropper that appears in master)
Merge pull request #169 from gnome-integration-team/download-experiments

Download experiments branch merged!