Re-factor `filter` operation internals

Because the Node.js Selenium API is currently unable to schedule
operations in parallel, querying multiple DOM elements requires far too
much time.

Instead, use a single querying operation to count many elements.
Temporarily unset the driver's `implicitlyWait` parameter so that
querying operations which yeild zero results can terminate immediately.
Move in-line selectors to dedicated file
Implement proxy for integration tests

This can be used to speed up tests by short-circuiting requests to
third-party services.