ENYO-3416: [DO NOT MERGE] Add drop contraints for DnDed Components in designer mode

Related JIRA: https://enyojs.atlassian.net/browse/ENYO-3416, https://enyojs.atlassian.net/browse/ENYO-3425

Contraints about components DnD in Designer and ComponentView have been added
.design files for enyo and onyx are available in https://enyojs.atlassian.net/browse/ENYO-3416 to match this mecanism
The goal of this PR is to validate contraints definition and mecanism

enyo.TableCell receive a default content, onyx.Picker and onyx.IntegerPicker default components.
enyo.Table and enyo.TableRow have their content hidden

Enyo-DCO-1.1-Signed-off-by: Vincent HERILIER vincent.herilier@hp.com