When previewing a page creation, populate url_path.

This ensures that Page.dummy_request can infer a sensible hostname rather than falling back on example.com, which fails when ALLOWED_HOSTS is enforced.
When generating dummy requests for pages with no routable URL, fall back on a hostname from ALLOWED_HOSTS and finally localhost
Changelog entries for dummy_request fixes
Fix #94. Panels are now hidden on page load if they are marked as
deleted after a form validation failure.
Changelog entry for a5072c7
Merge branch 'stable/0.3.x'

Conflicts:
	CHANGELOG.txt