Improve submission page

[karthikv]

• [x] escape button to get out of modal
• [x] resizing
• [x] remove first sentence under submit homework
• [x] consider elucidating "map submission"
• [x] remove "your pdf has been uploaded; " say "we've record your subission time: ____"
• [x] "Please choose which questions you answered on which pages"
• [x] make selection border thicker
• [x] put question and part in header near "Select Pages"
• [x] mention "you have not mapped all parts yet"
• [x] change "Homework" to "View"
• [x] no answer to question

[karthikv]

Done.