Opt-in PB donation w/ payment via heart button

[Klakurka]

To not piss anyone off, let's add a small button in the bottom of the dialog/widget somewhere that configures the bonus BIP21 output for the PB donation %.

Possible idea:

Of course the default will be set by the button config.

Also, let's save this in local storage or something if we can so that if they set it once on a site then it will be on/off by default when they come back or make another payment (remember the % too if on).