Implement WikiPage.getVersion(versionName). Will replace getDataVersion().
Replace invocations of getDataVersion() with getVersion().
Move PageData.getXrefPages to WikiPage. Make TestPage a subtype of WikiPage.
Needed the last change to make sure the page rendering does not distinguish between Wiki and Test pages
Get ParsedPage from WikiPage via special interface.
Build ref pages and class path via WikitextPage interface.
Move getHeaderPage and getFooterPage out of the WikiPage interface, into WikiPageUtil.
Let symbolicPage return a default (empty) parsed page.
Remove WikiPage.readOnlyData(). Just use getData().