Story Metadata

* Moved the "identity" and "description" story values out of the
StorySettings into a 'story metadata' section, editable from the Story
Menu. These each insert <meta> tags into the built HTML's <head>,
regardless of story format.
* Altered the 'blank CSS' StorySetting's implementation to remove the
default CSS <style> tag at compile time, not runtime.
* Fixed an engine crash when trying to serialise a cyclic object. Now, a
cyclic check has been added, and all cyclic object cloning and
serialisation will silently fail (much like non-serialisable functions
will silently fail).