[FIX] remove an useless <div> in searchview drawer
[FIX] fix various issues with the drawer (addon web)

* separate the css class oe_searchview_custom into oe_searchview_custom
and oe_searchview_savefilter to be able to style them independently
* by default, the drawer has display:none
* fix a bug occuring when the user removed a custom filter (it hid the
remaining filters)