Modify container API response to better work with ExtJS

* Include container ID.
* Add leaf virtual property.
* Rename "children"  to "data".
* Create minimal ExtJsResponse class to modify response content when necessary.
Add colour property to container entity
Include the sample capacity in the container API response
Add user and container fixtures

* Add hautelook/AliceBundle
* Remove ResearchGroup value object to make fixture generation easier
* Generate fixtures - users are in YAML as they do not have relationships; containers are in PHP as the relationships are a little complicated due to the hierarchy and container/sample container type.
* Modify container colour migration to store hash prefix for hex colour.
Merge pull request #12 from littlerobot/feature/6-container-database

Use container data stored in database to populate tree view