Fixed bug causing the page name to be changed to 'on' when using the switch for auto-reload of a page preview after having changed the name of a page in its preview tab
Increase page version on all element changes and if page itself is changed.
Major improvements for the preview handling:
- On changes, update only active (=visible) preview page
- Update preview only if page has a new version (and keep track of page versions in the UI)
- Correctly handle deletion of a page now (remove tab, preview iframe, activate other tab if necessary)