[simple theme] refactor search form

* update search input form params; inspiried by whoogle
* remove autofocus from result page input form (JS impl. as well as input param)
-> autofocus on landing page still works only on desktop and tablet with JS impl.
* update landing page margins on mobile
* rework border and radius for search form to 0.8rem and outline
* remove positioning from autocomplete JS lib and use CSS impl.
* match search box and autocomplete width
* rework search form to a google like design on mobile
* fix settings icon display withg RTL on mobile on result page when search input is empty

searx/static/themes/simple/src/less/index.less

@@ -49,9 +49,3 @@
     margin-top: 6em;
   }
 }
-
-@media screen and (max-width: @phone) {
-  #main_index {
-    margin-top: 0;
-  }
-}