Change select boxes to radio buttons for mapping type selection

- Radio buttons make switching between types when editing a mapping
  easier. It's one click rather than 2/3, and you can see the options
  sooner. This has been a minor usability problem in user research.

(Thanks to @elliotcm for helping to get the JavaScript working with radio buttons.)
`type == 'unresolved'` needs to handle an existing record. I can't try it right now, but this could work:
```ruby
<% checked = @batch.type || (type == 'unresolved') %>
<%= radio_button_tag(:type, type, checked, class: 'js-type') %>
```