Added plugin to allow content editing in modals.

Allows editing of multiple existing content items.
Content node labels update when modified.
Merge branch 'master' into edit-modals
Added editing to the editing demo page

Removed editing from the example demo page
Updated knowledge-graph.js dist
Merge branch 'master' of https://github.com/knowledge-graph/knowledge-graph
Updata knoeledge-graph.js dist