Fix broken images, hyperlinks, HTML and spelling.

- Fix a bunch of typos and tiny HTML errors.

- Fix broken image references in minting page.

- Fix invalid protocol-relative links; the ones changed to HTTPS were
  ones where either the HTTP redirected to the HTTPS or where the HTTPS
  was fully valid.

  The ones changed to HTTP were where there was no or an invalid HTTPS
  certificate or an otherwise broken site (All Things Luxury, mixed mode
  content breaks their HTTPS site’s layout on some browsers); if
  peercoin.net were being served across any protocol other than HTTP
  (i.e. HTTPS), these links would have been broken.

- Changed other domain-level redirect to the canonical URL.