Renamed all the XUL elements to have a long prefix on all cases
('unifiedsearch-'), and for elements with subelements, sub-prefixes
(like 'unifiedsearch-widget-', 'unifiedsearch-widget-bar'..)
following the hierarchy when need.
This fix the latest review notes at AMO by [Kent James] (https://addons.mozilla.org/es/firefox/user/rkentjames1/)
[review] (https://addons.mozilla.org/es/developers/addon/unified-search-187593/versions/1301380)