grunt: add jquery plugins

* Add missing datepicker.css, theme.css and
  ui-bg_flat_75_ffffff_40x100.png

Signed-off-by: Pedro Gaudêncio <pedro.gaudencio@cern.ch>
Reviewed-by: Javier Martin Montull <javier.martin.montull@cern.ch>
search: fix css file path

* File on css/typeahead.js-bootstrap.css has
  the wrong path
 Signed-off-by: Pedro Gaudêncio <pedro.gaudencio@cern.ch>
 Reviewed-by: Javier Martin Montull <javier.martin.montull@cern.ch>