This fixes a small bug with wikis where the dropdown label wasn't
updated correctly when switching the protocol.

Since we want to reuse this for group wikis, this also generalizes the
code a bit by:

- Moving the JS initializer into its own file.
- Moving the wiki specs for the clone panel into shared examples, and
  extending it to verify the dropdown switching behaviour.
- Using `container` rather than `project` in variable names.
- Using `repositories` rather than `project code` in UI strings.
- Renaming `enabled_project_button` to `enabled_protocol_button`, to
  make the intent clearer.