Add root field to ES backend
Django model field for root field
Django model for regs now list all root versions
Elastic Search backend allows listing root regs
Listing methods for regulations provide pairs of (version, label)
Add regulation (without a label) as an end point for listing all versions of all regs
Group by effective date per reg part
Merge pull request #35 from cmc333333/list-all-regs

Allow all versions of all regs to be listed