Merge pull request #383 from xschildw/remove-portal-endpoint

Remove portal endpoint from stackConfig
fix challenge overview page
Merge pull request #388 from jay-hodgson/release-z

fix challenge overview page (merge from release-y)
SWC-605: set load listener before setting url, and use HIDDEN style to fix calcuation
SWC-605: block Image widget editor insertion of markdown unless the file extension is right.  suggest png or jpg for images
Merge pull request #390 from jay-hodgson/release-z

SWC-605: merging up to release-z from develop after re-evaluation of impact/risk
Merge branch 'release-z' into develop