Merge pull request #146 from jonnor/fixup-journal-docs

Journal: Document a bit better in code and CHANGES
Typo fix
Merge branch 'master' of github.com:noflo/noflo
Fix legacy exports only if they're actually in legacy format
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