refactor(compiler): remove Viewport directives, use Decorator instead

BREAKING_CHANGE:
- The special type of `Viewport` directives is removed
  in favor of a more general `Decorator` directive
- `ViewContainerRef` now no more has a default `ProtoViewRef`
  but requires an explicit one when creating views.

Closes #1536

modules/angular2/src/render/api.js

@@ -91,7 +91,7 @@ export class ProtoViewDto {
   // The view of the component
   // Can contain 0 to n views of type #EMBEDDED_VIEW_TYPE
   static get COMPONENT_VIEW_TYPE() { return 1; }
-  // A view that is included via a Viewport directive
+  // A view that is embedded into another View via a <template> element
   // inside of a component view
   static get EMBEDDED_VIEW_TYPE() { return 1; }
 
@@ -111,7 +111,6 @@ export class ProtoViewDto {
 export class DirectiveMetadata {
   static get DECORATOR_TYPE() { return 0; }
   static get COMPONENT_TYPE() { return 1; }
-  static get VIEWPORT_TYPE() { return 2; }
   id:any;
   selector:string;
   compileChildren:boolean;

modules/angular2/src/render/dom/compiler/directive_parser.js

@@ -56,11 +56,7 @@ export class DirectiveParser extends CompileStep {
       cssSelector.addAttribute(attrName, attrValue);
     });
 
-    var viewportDirective;
     var componentDirective;
-    // Note: We assume that the ViewSplitter already did its work, i.e. template directive should
-    // only be present on <template> elements!
-    var isTemplateElement = DOM.isTemplateElement(current.element);
 
     this._selectorMatcher.match(cssSelector, (selector, directiveIndex) => {
       var elementBinder = current.bindElement();
@@ -87,26 +83,12 @@ export class DirectiveParser extends CompileStep {
           elementBinder.readAttribute(attrName);
         });
       }
-      if (directive.type === DirectiveMetadata.VIEWPORT_TYPE) {
-        if (!isTemplateElement) {
-          throw new BaseException(`Viewport directives need to be placed on <template> elements or elements ` +
-            `with template attribute - check ${current.elementDescription}`);
-        }
-        if (isPresent(viewportDirective)) {
-          throw new BaseException(`Only one viewport directive is allowed per element - check ${current.elementDescription}`);
-        }
-        viewportDirective = directive;
-      } else {
-        if (isTemplateElement) {
-          throw new BaseException(`Only template directives are allowed on template elements - check ${current.elementDescription}`);
-        }
-        if (directive.type === DirectiveMetadata.COMPONENT_TYPE) {
-          if (isPresent(componentDirective)) {
-            throw new BaseException(`Only one component directive is allowed per element - check ${current.elementDescription}`);
-          }
-          componentDirective = directive;
-          elementBinder.setComponentId(directive.id);
+      if (directive.type === DirectiveMetadata.COMPONENT_TYPE) {
+        if (isPresent(componentDirective)) {
+          throw new BaseException(`Only one component directive is allowed per element - check ${current.elementDescription}`);
         }
+        componentDirective = directive;
+        elementBinder.setComponentId(directive.id);
       }
     });
   }