Aria role search instead of form

Currently search forms have a <code>role="form"</code> and the input boxes have a <code>role="search"</code>.

The specs (http://www.w3.org/TR/wai-aria/roles#search) state:
> search (role)
> A landmark region that contains a collection of items and objects that, as a whole, combine to create a search facility

And (http://www.w3.org/TR/wai-aria/roles#form):
> form (role)
> ...
> For search facilities, authors SHOULD use the search role and not the generic form role.

Therefore we should drop the <code>role="form"</code> and move the <code>role="search"</code> to the <code>form</code> element on search related forms