Add tablet media query configuration to renderer styling store

[brendan-cheong]

Would it be possible to have control over the media query that determines whether the device is a tablet (or larger) and the form displays with the tabbed layout (with the tab list displayed as side navigation) or collapsible layout (with the accordion)? At the moment, it is hardcoded to: theme.breakpoints.up('md').

We can work around this by setting the 'md' breakpoint in the theme to control this, though that obviously has a wider effect on how the renderer displays.