Enhance search form accessibility

Added field description via the title attribute and set to "required"
the search terms, as there is no reason to look up an emtpy string.

lang/en.yml

@@ -3,5 +3,6 @@ en:
     GOTO: 'Go to {page} page'
     TOC: 'Table of contents'
     Search: 'Search'
+    SearchTitle: 'Enter the terms to search'
     RESULTS: 'Showing results for "{query}" ({count} pages found):'
     NORESULTS: 'No results containing "{query}" were found.'

lang/it.yml

@@ -3,5 +3,6 @@ it:
     GOTO: 'Vai alla pagina {page}'
     TOC: 'Indice'
     Search: 'Cerca'
+    SearchTitle: 'Inserire i termini da ricercare'
     RESULTS: 'Visualizzazione dei risultati per "{query}" ({count} pagine trovate):'
     NORESULTS: 'Nessuna voce contenente "{query}" è stata trovata.'

templates/SearchForm.ss

@@ -1,6 +1,6 @@
 <form class="navbar-form form-search pull-right" $FormAttributes>
 	<div class="input-append">
-		<input name="Search" type="text" class="search-query input-medium" value="$SearchQuery">
+		<input name="Search" type="text" title="<%t Silverstrap.SearchTitle %>" required class="search-query input-medium" value="$SearchQuery">
 		<button type="submit" class="btn btn-primary"><%t Silverstrap.Search %></button>
 	</div>
 </form>