Core fix for bug 1104: ceci-definition element

1. Added <ceci-definition> which reads and parses ceci definition JSON blobs.
2. Changed lookups in ceci-designer to use CeciDefinitions instead of CustomElements.
3. Removed overkill checks for ceci definitions in ceci-element-base.
4. Allowed component-tray to only loop through CeciDefinition to avoid nonsense in ceci-element-base.