Make required field asterisk more prominent

[xmedr]

Overview

Help to make required fields more obvious by adding a note at the top of the form mentioning required fields, changing the color of the crispy form's asterisk, and increasing the font size a bit.

Closes #87

Demo

Testing Instructions

• Navigate to an "Add New \<Document>" page (i.e. http://localhost:8000/surveys/create/ )
• Confirm that the required asterisks stand out more