various changes to checkout page

various changes to checkout page

- disable quick receipt button unless at least one
  checkout has been made
- change the Done button to a button + dropdown allowing
  for ending the session with no receipt, a printed receipt,
  an email receipt, or an automatically generated receipt
  based on the user's preference
- use the btn-default style for the quick receipt button
- add explicit email option to the quick receipt dropdown
- display toast upon sending an email receipt

Signed-off-by: Galen Charlton <gmc@esilibrary.com>