2891: Workbench integration tests cope when screenshots aren't supported.
2891: Workbench handles expired tokens more consistently.

Previously Workbench would behave differently depending on whether an
expired token was provided as a query parameter, or living in a
session.  This makes it do the same thing in all cases.  It also fixes
some small bugs around removing api_token from URL paths.
2891: Workbench error page shows login status.

The tests here check that an error page shows the usual user
information for someone logged in, and renders okay for someone who
isn't.
2891: Refactor Workbench API token filters.

Remove dead code and simplify the implementation, especially the
relationship between the "required" and "optional" filters, per
discussion with Peter.
2891: Rename and comment Workbench API token filters.
Merge branch '2891-workbench-errors-retain-login'

Closes #3032, #3074.  Refs #2891.