Changed unit identifier to be readonly, not disabled

STUD-863

cms/templates/unit.html

@@ -182,7 +182,7 @@ require(["domReady!", "jquery", "js/models/module_info", "coffee/src/views/unit"
             <div class="row wrapper-unit-id">
               <p class="unit-id">
                 <span class="label">${_("Unit Identifier:")}</span>
-                <input type="text" class="url value" value="${unit.location.name}" disabled />
+                <input type="text" class="url value" value="${unit.location.name}" readonly />
               </p>
             </div>
             <ol>