This introduces ember-a11y-testing to acceptance tests via a helper
wrapper that allows us to globally ignore rules that we can address
separately. It also adds fixes for the aXe rules that were failing.
Changing namespaces can be done anywhere in the app even though many
Nomad resources aren't namespace-sensitive (e.g., clients, plugins).
A user changing namespaces is an intent to reset context, "now I want
to begin a task that relates to Namespace X". Where that task begins
used to always be the Jobs list, since it was the only namespace
sensitive resource. Now with CSI Volumes, "square 1" is Volumes if the
namespace is changed from a storage page.
