union-1016578: s/isSelection/hasPredictions/g

More and more things are lying about if they are a selection type, so it
is time to admit that this is really about if there are predictions.

Signed-off-by: Joe Walker <jwalker@mozilla.com>
union-1016578: 2 minor fixes to helpers.js

The new promises library requires you to use an array in Promise.all()
and make sure we clear the input in the failure case as well as the
success case.

Signed-off-by: Joe Walker <jwalker@mozilla.com>
union-1016578: Minor fix in union type

Signed-off-by: Joe Walker <jwalker@mozilla.com>
union-1016578: Add host.createUrl function

"new URL" is a standard that isn't well supported everywhere.

Signed-off-by: Joe Walker <jwalker@mozilla.com>
union-1016578: Update url type to provide better predictions

Uses host.createUrl to do this.

Signed-off-by: Joe Walker <jwalker@mozilla.com>
union-1016578: Improve unit tests for url type

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