Force login for downloads and other bug fixes

Requires AtlasOfLivingAustralia/ala-web-theme#5 be merged and built first.
Fixes #1 closing stream incorrectly
Fixes #2 Paging links for record downloads are squashed together
Fixes #4 Force login for downloads
Adds ability to add a Download that doesn't support HTTP HEAD requests
Adds ability to add a Download that doesn't support HTTP ETag and Last-Modified headers
Add optional support for Content-MD5 header
Add MD5 calculation for requests that don't support HEAD, ETag, Last-Modified and Content-MD5 headers