ui: fixes for combar and smartlist

- the background under item hovered is now correct.

- using wheel mouse over the smartlist is fixed.

- config screen bug fixed.

- the combar has the good behaviour when using the scrollbar of the smartlist

Change-Id: I5010e0b93a8361f3bbf387317c9a00374222547f
Tuleap: #286
Tuleap: #288
Tuleap: #289