Add [spoiler] bbcode tag support

Sometimes, when discussing pop culture, we want to be able to hide
information from casual perusal so that other users will know that
reading on may reveal information that they do not want to learn early
(spoilers). BBCode markup on GaymerConnect may now wrap such sensitive
information with a [spoiler] tag.

The Ruby BBCode implementation is fairly easily extensible, so adding
this tag for server side rendering just entailed updating an
initializer. The JS implementation is not quite so kind. I have
unvendored jquery.bbcode.js in order to patch it to add the 'spoiler'
button to the layout.

To update the JS side bbcode implementation, it was necessary to
seperate bbcode.js, which previously had a minified version stuffed on
top of jquery.bbcode.js. I'm now treating it as an explicit include via
the Rails asset pipeline.