reduce duplication and code improvements (#1707)

* reduce code duplication

* reduce duplication, fix license headers

* simplify code

* typings fixes

* update tests

* minor fixes

* markdown fixes

* revert changes

docs/extending/registration.md

@@ -17,7 +17,7 @@ and use the following snippet to register custom content:
 import { ExtensionsModule, ExtensionService } from '@alfresco/adf-extensions';
 
 @NgModule({
-    imports: [ ExtensionsModule ]
+    imports: [ ExtensionsModule ],
     declarations: [ MyComponent1, MyLayout ]
 })
 export class MyExtensionModule {