FEATURE: uses select-box for topic-notifications-button component

- Introduces ComponentConnector to use a component inside a widget
- Use css to set size of components instead of properties
- Smarted positionning
- Style tweaks

test/javascripts/components/select-box-test.js.es6

@@ -222,7 +222,7 @@ componentTest('persists filter state when expandind/collapsing', {
 });
 
 componentTest('supports options to limit size', {
-  template: '{{select-box maxCollectionHeight=20 content=content}}',
+  template: '{{select-box collectionHeight=20 content=content}}',
 
   beforeEach() {
     this.set("content", [{ id: 1, text: "robin" }]);