#1754: better keyboard controls for tipping
#1754: better keyboard controls for tipping

Now:
+ pushing enter submits your change
+ pushing escape cancels the change
+ when the user starts typing and then pauses for 1 second, the input
is validated again (enabling the "confirm" button)

studio666/gratipay.com,gratipay/gratipay.com,eXcomm/gratipay.com,studio666/gratipay.com,mccolgst/www.gittip.com,mccolgst/www.gittip.com,gratipay/gratipay.com,eXcomm/gratipay.com,gratipay/gratipay.com,eXcomm/gratipay.com,eXcomm/gratipay.com,studio666/gratipay.com,mccolgst/www.gittip.com,mccolgst/www.gittip.com,studio666/gratipay.com,gratipay/gratipay.com