Improved work request view with tabs like the artifact view

We should improve the work request detail view both for work requests and workflows, and harmonize it with the new tab-based artifact view. Here's a proposal for the various tabs:

• Any task-specific view
• Workflow: (for workflows only, their default view) the tree of work requests, for a non-root workflow it should have the ancestors workflows up to the root one.
• Work request: (for any work request, including workflows)
  • a description of the work request together with a list of the input artifacts
    • that description should probably be overridable for each task so that we can give a human-friendly summary of the task_data
  • a summary of the result (can be overridden by each task so that we can give some more details than just)
  • the information currently shown in the side panel + a list of the ancestors workflows.
• Output: list of generated artifacts + work_request.output_data
• Dependencies: this should list all the work requests that the current work request depends on, as well as the list of work requests that depend on the current work request.
• Internals:
  • the metadata
  • the event reactions
  • the output_data field
  • the workflow_data field

Arguably, when an error is returned in work_request.output_data, it should also be shown in the main "Work request" view, possibly close to the "Result: Error" badge.

Implementation plan

• Implement the new generic WorkRequestView to use tabs (same as ArtifactView in !1722 (merged))
• Migrate LintianView to add the specialized tab
• Migrate AutopkgtestView to add the specialized tab

Considerations for the Autopkgtest view

The presentation of the results should be improved. We want a clear table with a list of the tests and their results and ideally direct links the correct place inside the "structured log browser" (cf #810). The link to the artifact with the results should also have a clear indication that it's a link to an artifact (we really need/want a standardized representation here, a widget? a template tag?).