Modified some views, routes and models to work with the new many-to-many for tests and benchmarks

views/test/add.twig

@@ -23,8 +23,8 @@
 
         <div class="four columns">
           <label>
-            Benchmark:
-            <select class="u-full-width" name="test_benchmark">
+            Benchmarks:
+            <select class="u-full-width" name="test_benchmarks" multiple>
               {% for b in benchmarks %}
                 <option value="{{ b.id }}">{{ b.name }}</option>
                 {% endfor %}