A wrapper for the generated `ApiClient` class tracks the number of running
queries. This makes it much simpler to show the "API calls pending" UI
element, regardless of which part of the webapp performs the queries.
For task scheduling this doesn't matter, but for human workflow it can be
useful to differentiate between "failed" (and should be retried) and
"cancelled" (no longer relevant).
Add a bar for "job actions", i.e. buttons that do something with the
selected job(s).
Just has one button, and it doesn't do much either, but at least the
framework for these things is here.
