Make the layout adjust to narrow viewports better

Make the layout adjust to narrow viewports better

Below about 600px (phones and small windowed browsers) the sidebar
starts breaking the layout. Moving it inline helps a lot; with
modern CSS (flex layout) we can also shuffle it after the main content.
Older browsers that don't do one of the 4 variants of flex layout
will just display it above the main content, which is annoying
but not too bad.

blueview also has a minimum width set so that it won't become
ridiculously small with small fonts, but that means it gets
scrollbars below about 850px; stop enforcing the minimum width
if necessary.

Finally, blueview's relatively generous margins look good in a
desktop browser, but are just too space-hungry on a phone.
Turn them off below 600px.