[ADF-814] application configuration service (#1969)
[ADF-814] application configuration service (#1969)

* app configuration service

* api improvements and readme update

* extend readme and add defaults

* unit tests for app config service

Alfresco/alfresco-ng2-components,Alfresco/alfresco-ng2-components,Alfresco/alfresco-ng2-components,Alfresco/alfresco-ng2-components