Distributor: UI bug: switching set up process doesn't clear fields

Describe the bug
From @helen's comment on #368:
UI bug - if I click "Manually Setup Connection" but then decide to switch to WordPress.com Application, the fields do not disappear. See screenshot for what I mean. I think this should probably reset entirely, so hide the fields when you switch, but if you switch _back_ to Username/Password it should give you the wizard thing again.

Steps to Reproduce

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior

Screenshots

Environment information

• Device:
• OS:
• Browser and version:
• Distributor version:
• Theme and version:
• Other installed plugin(s) and version(s):

Additional context