Update base.html

Update links to https
Update account_signup.html

Update links to https
Merge pull request #122 from J0WI/master

Updated links to https
Fix bug 1015542: Collapse sandstone migrations into single file.
Merge pull request #124 from Osmose/sandstone-migrations

Fix bug 1015542: Collapse sandstone migrations into single file.
Fix bug 1019227: Embed prototype agreement as PDF.

Renames Agreements to SignedAgreements and adds an Agreement model to
store different versions of the agreement. The agreement is now stored
and displayed as a PDF using PDF.js.