The old behaviour meant that resizing the base font resized every page
element in proportion. The new behaviour makes the text resize within a
fixed layout, so that one can alter the number of characters displayed
on each line of a tiddler. The old behaviour can usually be emulated by
using the browser page zoom tool.
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
