Improve usability of form for adding a consumer

Problem/Motivation

When you go to create a new consumer (admin/config/services/consumer/add), if you have not already created a role that's valid to use with the new consumer, it can be a frustrating experience. You fill out the form, but don't realize you need to have a role defined that can be used for the "Scopes" section until you get to the bottom of the form. The have to go off, create a role. And then navigate all the way back, and fill the form in again. It's not really that big of a deal, but this has been an issue for me at least enough times that I was compelled to say something about it.

Proposed resolution

Ideally users are alerted to the fact that they need to create a new role before they can proceed before they've filled out the form already and then have to loose the work they've already done. This could be done by adding a notice to the top of the page. Or maybe better, just don't display the form and show only a message asking the user to create a role first. With a link to do so that ideal redirects back to admin/config/services/consumer/add.

Remaining tasks

User interface changes

API changes

Data model changes