Replace PayPal button with Gratipay
Replace PayPal button with Gratipay

Fixes #461

radiant-player/radiant-player-mac,kbhomes/radiant-player-mac,radiant-player/radiant-player-mac,radiant-player/radiant-player-mac,kbhomes/radiant-player-mac,radiant-player/radiant-player-mac,kbhomes/radiant-player-mac,kbhomes/radiant-player-mac,kbhomes/radiant-player-mac,radiant-player/radiant-player-mac