Store judge prize preferences

[ben-m-young]

Right now JudgesProject keeps track of which judges score which projects, but we don't yet have a way to create that information (the data that's currently there was randomly generated).

• Add 3 new string-valued columns - FirstPrizeChoice, SecondPrizeChoice, and ThirdPrizeChoice to Judge. These should have foreign key constraints referencing prize_name in table Prize.
• Add 3 dropdown inputs to judge_registration_form.html (which gets rendered on register/judge after you click "Register to be a judge" on the main page) asking which prizes/tracks they would like to be a judge for. Each dropdown should contain the list of prize names stored in the table Prize. The 3 dropdowns ask for their first, second, and third preferences, respectively.
• Insert the data from these new inputs into the 3 new columns in Judge upon submission.