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
Merge pull request #364 from edpaget/private-groups

Add private flag to UserGroups
Add state description to membership docs

Closes #371
Fix roundness typo

Closes #374
Convert to new Locations Format

Locations becomes an array of available media. Create and Update
methods accept an array of mime types. If a particular peice of media
has multiple representations they should be sent as a comma-seperated
string of mime types.

Examples:

two jpeg images

```
"locations": ["image/jpeg", "image/jpeg"]
```

A single video encoded multiple ways

```
"locations": ["video/webm,video/mp4"]
```

Closes #369 Closes #341
Merge pull request #380 from edpaget/fix-workflow-docs-typo

Fix roundness typo
Merge pull request #379 from edpaget/update-membership-docs

Add state description to membership docs