Tweaks to control panel and theme tweaks

Courtesy of @giffmex
Add font family to the Snow White theme tweaks
Restore missing opening `<html>` tag

Astonishingly, the templates have accidentally omitted the opening tag
for some time. There were no ill effects, because browsers obligingly
add it back in when parsing
Bail out earlier when displaying a modal for a non-existent tiddler
Remove reference to TiddlyMall

Because it doesn't exist. (It was a suggestion from @giffmex that got
inadvertantly included)
Fix up the sample wizards

They stopped working because the "Demos" tiddler went away
Add tiddlers for Press and Examples
Fix crash on processing anonymous macro parameters

Fixes #151
Missing slash