Issue #2352155 by Wim Leers: Remove HtmlFragment/HtmlPage.
Revert "Issue #2232477 by tstoeckler, a 'fliptable' mateescu, plach: Fixed Fatal when adding new fields with NOT NULL constraints in a base table that contains existing entities."

This reverts commit 08d3ebba69520f2e800323709201d85c9c80527c.