Objectives to be done before release for testing

[katjad]

Another parent ticket - want to do these till "beta release"/MVP (end of March hopefully!!):

• Account management, so users can update username, email, password (was alerted to this by someone and is actually a must-have, I think)
• Internal messaging for arranging "handover" of books, rather than giving people each others' emails
• Display flash messages, for example when somebody has requested a book
• Improve styling (book grid, profile page)