Submit button should not overlap the footer.

Whenever someone select a theme that add or remove pickers, the height
of the preference panels should be adapted or the button will overlap
the footer.

This is part of story #6003: be able to change the Experimental theme
color

Change-Id: Ic823a0cfd21cc1cd63237feefd3682f8546e5b25
Merge commit 'refs/changes/15/2715/1' of ssh://gerrit.tuleap.net:29418/tuleap into HEAD

* ssh://gerrit.tuleap.net:29418/tuleap:
  Submit button should not overlap the footer.

Change-Id: Id812b280bc29df3588e372787dccbb14188ab4fd
This is Tuleap 7.2.99.17

Change-Id: Ie0604587c3c381fff8af71544a6dc003d7ed30dd