Fix quoting again

Fix quoting again

Quoting now properly converts all div.fquote/span.fspoiler/blockquote
tags back to their postable GameFAQs equivalents. DOM is used to do all
this, since regex isn't very robust when it comes to HTML parsing.

Signatures are now removed by removing the span.gamefox-signature
element instead of using a regex - this feels like a cleaner solution
but relies on the elements.sigspans pref to be true. Hopefully that
isn't much of an issue because 99% of people should have that pref set
that way.

(Remaining quote issues will be fixed in another commit.)