BUG: refs #1060. Fix midas.empty css and js

Commit 8bab69c and 248297f fixing issue #994 forgot
to update the midas.empty css and js. This was having
undesired side effect on page using the empty
layout (for example the Slicer appstore).

This commit fixes the issue back-porting the changes
associated with 8bab69c and 248297f to midas.empty.(css|js)

Signed-off-by: Patrick Reynolds <cpreynolds@gmail.com>
Merge branch '1060-FixEmptyLayout-jcfr'

* 1060-FixEmptyLayout-jcfr:
  BUG: refs #1060. Fix midas.empty css and js