Jasmine tests for verification / payment; small bugfixes

* Add Jasmine tests for a good chunk of the payment/verification JavaScript.
* Found and fixed a bug: the payment button should be enabled if there are no suggested prices (and no radio buttons).
* Some general cleanup / refactoring.

Reviewers: @rlucioni @AlasdairSwan 
This is the smallest of nitpicks, but we seem to have established a convention of using single quotes in our JS. For example, you use them in intro_step_view.js; it might be good to be consistent and use them here as well.