Journal: Fix typo and missing implementation for changeEdge
Graph: Emit metadata changes on node/edge/ports removal

Needed for the journal to be able to restore metadata when undoing removals.
Fixes noflo/noflo-ui#96, undoing node removal resets position to 0,0
Merge pull request #148 from jonnor/fix-metadata-on-undoing-remove

Fix metadata on undoing remove