Improve mobile styling for Create Rubric page

[karllhughes]

What?

There should be an alternate view for creating rubrics when on mobile. We have a similar "alternative" view for viewing rubrics on mobile, so you may want to look at that.

Why?

Creating a rubric in our current mobile view is cumbersome because you have to horizontally scroll a lot.

How?

Mockup

• This is very rough, but I'm thinking something like this: https://docs.google.com/drawings/d/1gCvVPOaHLv7-N6E7POndVSH0xJIwHSyB1bIpio9-8XU/edit?usp=sharing

User stories

• As a mobile users, I can create a rubric without scrolling horizontally.
• As a desktop user, I can create a rubric in the existing interface

Resources

• Might want to use Bootstrap collapse: https://getbootstrap.com/docs/4.0/components/collapse/