Fix GRE score report when there are no scores.
Page types which do not implement the StatusPage interface shoudl not be able to set showAnswerStatus to true or even if it is true be displayed on the status page.
Merge pull request #239 from jrjohnson/textpagestatus

Enforce page status interface
Better status pages for standard page descendants.
Fix issues in [6f20f61c67e490884bbf467e0d7b496e131aea49].
Prevent branching page from showing answer status.
Prevent QAS page from showing answer status.
Working status page for Education page.
Merge pull request #240 from jrjohnson/fix-status-pages

Better status pages for standard page descendants.