Pull in updates to email groups
Update nav to use email_groups data

Previously, the email groups were coming from _data/private/nav_links.yml,
even though email_groups.yml existed. Gray Brooks submitted a PR to update an
item in email_groups.yml, but the change didn't translate into an update to
the generated website. Now, email groups have been removed from nav_links.yml,
and this change now updates the "Email Groups" section of the nav bar with
data from email_groups.yml.
JoinerImpl.remove_private_data

Recursively removes private data from a Hash or Array. First step in
implementing Hub support for the new data schema that allows data nested
within "private:" fields to be filtered out in public mode.
Trailing whitespace, comment fixes
JoinerImpl.deep_merge
Merge pull request #12 from 18F/team-data-private-1

Implement deep Hash and Array merges