Install git in Docker build

Allows installing Gems from GitHub.
Allow searching of groups by name
Merge pull request #359 from astopy/docker-git

Install git in Docker build
Use add_relation instead of update_relation

the #update_links controller method previously calling the wrong method
to add links to a relation.

Closes #356
Add owner_name and links to user_group sample response

Closes #347
Merge pull request #357 from edpaget/filter-groups-by-name

Allow searching of groups by name
Merge pull request #360 from edpaget/fix-update_links-method

Use add_relation instead of update_relation
Add owner name to user responses
add subject bucket prefix path
Prevent CORS issues in dev
Merge pull request #363 from camallen/s3_subjects

add subject bucket prefix path
Merge pull request #361 from edpaget/update-user_group_docs

Add owner_name and links to user_group sample response
Merge pull request #365 from rogerhutchings/dev-cors

Prevent CORS issues in dev
Add private flag to UserGroups

Closes #355