Ability to filter Mistral items

Now we have some Mistral items such as workbooks, workflows, tasks and actions.

Workbooks and workflows have special parameter - tags that isn't used now. But we can use tags for filtering. For example we have a lot of workflows and we need to see only direct ones, in this case it would be great to have opportunity to choose them for example using CLI:
mistral workflow-list type=direct.

Another situation. We have a lot of 'standard' OpenStack actions and we will have more. So it is not very convenient to look through all of them to find actions for nova. In this case we can have smth like that:
mistral action-list type=nova

So, Need to implement filters on REST API endpoints which work with multiple items (such as /tasks, /workbooks etc.)