A new flag and site-config option, to set the title/legend of the new-blog-entry form.

This adds a new flag to the blog syntax: `newentrytitle`

e.g. `{{blog>.?10&newentrytitle=New bulletin title:&topform&nofooter}}`

A couple of shortcomings:

1. The default (in whatever language) is not shown in the site config form (rather, this is blank unless customised); and
2. Ampersands cannot be used in the newentrytitle, because they are the flag delimiter.