feat #1724 Raising an event when a new parent is added in the 'aria:parent' property of a node
feat #1724 Raising an event when a new parent is added in the 'aria:parent' property of a node

This commit adds a new global `aria-parent-metadata-added` event
in `aria.utils.Json` which notifies that a new parent has been added
in the `aria:parent` property of a node of the datamodel.

This can help detecting potential memory leak issues with `aria:parent`
properties being added in the datamodel, but never removed.

close #1713 
close #1724
benouat/ariatemplates,ymeine/ariatemplates,benouat/ariatemplates,divdavem/ariatemplates,fbasso/ariatemplates,ariatemplates/ariatemplates,ymeine/ariatemplates,fbasso/ariatemplates,ymeine/ariatemplates,ariatemplates/ariatemplates,divdavem/ariatemplates,benouat/ariatemplates,divdavem/ariatemplates,ariatemplates/ariatemplates,fbasso/ariatemplates