Fix next-question-button for smaller screens

Summary: I liked the word 'Awesome' too much to replace it enitirely, so if you have a smaller screen (or window < 1150p), you get 'Nice' instead. Admittedly doesn't work if you resize the window once it's been rendered, but I don't think that merits the on-resize trigger.

Test Plan: Tested on window size 1280 (Awesome) and size 1040 (Nice)

Reviewers: alpert

Reviewed By: alpert

CC: eater, alpert

Differential Revision: http://phabricator.khanacademy.org/D6207