Improve assessment form

[u8sand]

• [x] Improve auto-selection of similar urls (choose the closest matching/auto match if exact)
• [x] Allow users to login if they are not yet logged in
• [x] Enable search through entire database for selections though showing filtered options is still desired as a first pass
• [x] Make it look and feel nicer
• [x] Ensure validation happens properly
• [x] Pull up existing assessment if the same user is assessing the same thing

[u8sand]

SearchVector-related things moved to #50