Fixup recently introduced regressions in HTML, UX, HiDPI and HTTPS

* Turn image resolution back up to not look crap on HiDPI
  displays (follows-up I401a6436e).
* Fix insecure content-warnings for top-bar icon
  (follows-up Ib58979f0a).
* Removed added redundant self-closing slashed, omitted
  everywhere else already.
  Fix invalid leading slash in '</br>'
  (follows-up I1bc95c2fb, Ib324da1ff)
* Restore broken links when integration portal is mounted in a
  non-root directory (e.g. locally). Don't assume '/' is
  pointing to docroot.

Change-Id: Iac49f20c8aa034b466ff7addf6e2efbaa160d94c