Add a view of role assignments

Summary
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This blueprint will add a new table to provide a better view of role assignments.

Motivation
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Customers are asking for a view of role assignments so they can easily view the roles they have assigned to users and groups.

Description
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The new table will be placed on a second tab on the current Roles page called Role Assignments. The Role Assignments table will show the user / group / role / project / domain for each role assignment. Each resource can be linked to the corresponding (and already existing) detail page. The role assignments can be obtained using the following keystone v3 API: http://specs.openstack.org/openstack/keystone-specs/api/v3/identity-api-v3.html#list-effective-role-assignments

UX
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The UX for the new table should match the other angular identity tables.

Testing
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Nothing special here. There will be Jasmine unit tests.

Outside Dependencies
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The role assignments API currently returns only IDs for each resource. This is hopefully going to be updated to include both names and IDs so that we don't just have a big table of UUIDs. With a name and ID we can show the name and link to the corresponding detail page. There is some concern about the performance impact this could have on an already performance intensive API.

Requirements Update Required
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Possible, but I don't think so. We could simply fall back to showing only IDs if the API doesn't give us a name.

Doc Impact
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None