browser: voting, user info, answer, and SO link updates

browser: updates to account dropdown, contributor modal dialog
- make display consistent with wireframes (votes cast, etc.)
- fix associated tests

browser: updates to voting, vote acceptance
- move vote-related logic from controller to model (ssAnswer, ssQnaDoc)
- update button styles to be consistent with wireframes
- make voting update the user's votes cast

browser: require user to be logged in to answer questions

browser: add icon for linking to stackoverflow.com