fix(compiler, view): centralize TemplateElement checks and fix inconsistencies

Fixes #189
Closes #194

modules/facade/src/dom.dart

@@ -79,4 +79,7 @@ class DOM {
   static attributeMap(Element element) {
     return element.attributes;
   }
+  static Node templateAwareRoot(Element el) {
+    return el is TemplateElement ? el.content : el;
+  }
 }

modules/facade/src/dom.es6

@@ -78,5 +78,7 @@ export class DOM {
     }
     return res;
   }
-
+  static templateAwareRoot(el:Element):Node {
+    return el instanceof TemplateElement ? el.content : el;
+  }
 }