fix(render): allow to configure when templates are serialized to strings

Introduces the injectable `TemplateCloner` that can be configured via the new token `MAX_IN_MEMORY_ELEMENTS_PER_TEMPLATE_TOKEN`.

Also replaces `document.adoptNode` with `document.importNode` as otherwise
custom elements are not triggered in chrome 43.

Closes #3418
Closes #3433

modules/angular2/src/render/render.ts

@@ -9,4 +9,5 @@ export * from './dom/view/shared_styles_host';
 export * from './dom/compiler/compiler';
 export * from './dom/dom_renderer';
 export * from './dom/dom_tokens';
+export * from './dom/template_cloner';
 export * from './api';