Some users cannot list namespaces on a cluster. The add wizard showed
an error and offered no way forward.
The namespace step now switches to a text prompt when the list call
fails or returns nothing. The prompt shows the reason and checks that
the name is a valid DNS label. Esc from a later step returns to the
prompt.
The j and k keys now type into text fields. They moved the list cursor
before, so a name such as kube-system could not be typed.
Closes#66
