refactored TiddlySpaceRevisionView's styles caching
refactored TiddlySpaceRevisionView's styles caching

using jQuery's data method instead of awkward custom attributes

in the process, fixed repeated unnecessary invocation of jQuery wrapper
(though there are many instances of that left still)

This also appears to fix #469, preventing a seemingly random exception
from being raised.

FND/tiddlyspace,FND/tiddlyspace,TiddlySpace/tiddlyspace,TiddlySpace/tiddlyspace,FND/tiddlyspace,TiddlySpace/tiddlyspace