No UI for switching themes yet, try these two commands in the console:
`$tw.wiki.addTiddler({title:"$:/theme",
text:"$:/themes/tiddlywiki/starlight"})`
and
`$tw.wiki.addTiddler({title:"$:/theme",
text:"$:/themes/tiddlywiki/snowwhite"})`
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
