Eliminated <br> elements + added Jonah padding

* Jonah: added bottom padding to #passages, so that the present passage
isn't always uncomfortably flush with the bottom of the window.
* Also updated scrollWindowTo() to take a second "margin" argument.
* Wikifier no longer generates <br>s!! Instead, the white-space:
pre-line and white-space: pre-wrap CSS attributes have been added to
.passage and .storyElement. I hope this works as well as it seems to,
because it should simplify various HTML methods in Twine a little bit.
* Altered the MIME-type of ttf and otf to "application/x-font-..."
instead of "application/font-...". Also, unrecognised files are now
"application/octet-stream".
* Added an "identity" setting to StorySettings, which lets you specify a
noun to use for game interface dialog boxes (the restart confirmation,
the error dialog, etc.)
* Removed the unused initialText property from Passage objects, as well
as Passage.prototype.reset.
* To save a little startup time, image passages are no longer
obfuscated.