Polishing Style Changes, and Resize Responsiveness

-- Made modal fully (and cleanly) responsive to resizing (tabs, buttons, fields, window), [600px , very large)
-- Changed Default Rubric Feedback Prompt to not include space beforehand
-- Made "add criterion" button fall in line with standards
-- Standardized indentations for options, and their sub elements. Reads like bullet-points by 5px.
Just curious where 600px came from?