Added POST & GET one REST API endpoints for custom entity data.
added button delete/restore field to the page "edit field"
added alert
Added DELETE REST API endpoint for custom entity data.
POST REST API endpoint: added catching invalid entity class name exception.
Custom entity REST API: added GET LIST endpoint.
Custom entity Rest API: added permissions check
Custom entity Rest API: added PUT endpoint
Merge branch 'fix/rest-custom-entities-data' into umbrella-master
Merge branch 'fix/added-button-delete/restore-field' into umbrella-master