Reduce a bit of redundency in the Build file
Add a provenance field and maintenance event relation to doc unit descriptions. Closes #250.
Improvements to sign up process (closes #228 and #251)

 - Added dedicated data policy page (should be static but never mind)
 - Added submission time and blank-field (honeypot) checks to signup
   process
 - Broken out signup data and validation to its own model
Closer to a working stage. RJS still not active
Merge branch 'master' into play-2.3rc1

Conflicts:
	project/Build.scala
Delete dup main.js