union-1016578: Move the test command/converters to mockCommands

If they're in the main store of mock commands then it makes it easier
to try them out for real, and we can re-use the json types more.

Signed-off-by: Joe Walker <jwalker@mozilla.com>
union-1016578: Rewrite union.parse()

The old union.parse didn't pass on predictions when there was a match
that was valid, this one does. The bad news is that the UI doesn't
currently display predictions for valid inputs, but that's a separate
bug.

Signed-off-by: Joe Walker <jwalker@mozilla.com>
union-1016578: Add a url type

Signed-off-by: Joe Walker <jwalker@mozilla.com>