To start with, we move the current stylesheets into a theme plugin
called "Snow White". Wikis have to specify at least one theme in their
`tiddlywiki.info` file. Next we'll add a mechanism for switching
between loaded themes
The refactored plugin is `tiddlyweb2` for the moment. The idea is to be
able to use the same syncer with a different adaptor for syncing
changes to the local file system.