improved checkout.html and initial returns commit

todo: notify holdee(returns), testing
implemented return functionality
update return functionality

retrieves email in qresult and book info in qbook
implementation of checkout and return

checkout only one item at a time
return error coverage

returning a book that was never taken out
fixed book checkout db inconsistensy
implement overdue report
added success messages
overdue report shows more info
removed old overdue file
overdue implementation bugs