The trouble with the previous approach of storing several settings in a
single data tiddler was that it made it hard to introduce new settings.
Users who already have a custom copy of the settings/metrics tiddler
wouldn’t get the default settings. The new approach uses individual
tiddlers for each setting.
This commit also introduces a new theme tweak for the cutoff width for
switching between responsive views.
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.
