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.
Create initial Profile model

Move choices from UserRegistrationLeadForm to Profile model
Create or update Profile in UserRegistrationLeadForm.save()
More WIP