Small fixes: user About, group search paging, -c bounds, parse templates once !13

Stacked on !12; retarget to main once that merges.

• #14 The person branch of the about module was else if false since upstream; restored, with a seam for the profile fetch and a test that decodes a DeviantArt-shaped profile and checks interests, social links and registration age render.
• #15 Group search built offset=10*page after incrementing the page, skipping results 10 to 19. groupSearchURL computes it from the request's page; the nav bar shows the right current page.
• #18 -c checked len(args) >= 2 instead of that a value follows; skunkyart -x -c panicked. exit is a variable so the test can observe it.
• #20 ParseTemplates parses static/html once per loaded language at startup; ExecuteTemplate looks the set up by request language. A bad template fails at boot. Languages() is now used.

#16 was already fixed in !9. Seven new tests; lint clean; passes with and without -tags embed.

Closes #14 Closes #15 Closes #18 Closes #20