Complete page / post revision maint (#13)

- Fix log on redirection
- Move page handlers to its own file
- Add version to admin area footer
- Move generator to HttpContext extension property

src/admin-theme/wwwroot/admin.css

@@ -87,4 +87,8 @@ a.text-danger:link:hover, a.text-danger:visited:hover {
 }
 .mwl-revision-preview {
   max-height: 90vh;
+  overflow: auto;
+  border: solid 1px black;
+  border-radius: .5rem;
+  padding: .5rem;
 }