Hide service binding creds based on role

-Only shows for SpaceDeveloper or Admin role
-Add ability for other models to serialize the
same way with :redact key

[finishes #62436754]
CC now adds all env vars to to the diego.desire.app message

* Refactor AppObserver to use DiegoClient for staging rather than
  DiegoStagerTask

Signed-off-by: Ted Young <tyoung@pivotallabs.com>
Redact creds for service_instances based on role

-Also remove unecessary 'plugin' line from service_bindings
Model and spec for Service Usage Events

[#66608588]
Repository for Service Usage Event find / create

[#66608588]
Fixing a error messages in App matcher
Create a service usage event when managed service instance is created.

[#66608588]
Controller / action for Service Usage Event enumerate

[#66608588]
Oracle index names cannot be greater than 30 chars

[#66608588]
Model and Repo support User Provided Service Instance

[#71195632]
Refactored creation of service usage events

In addition to being created for managed service instances, service
usage events are now created for user provided services.

[#71195632]
Filter by service_instance_type

[#71195632]
Documentation for Service Usage Events

[#71195632]
Updated API checksum

[#71195632]
Creating DELETED service usage events

[#70315230]