Set label scale

[lcmcninch]

It looks like there isn't a way to set the font size of the button label. The Label object itself is stored as a "protected" member of the button object so you can hack it by setting _label.scale but that isn't ideal.

Assuming I'm not overlooking something obvious, I was thinking I could contribute a small enhancement that would provide either a set_label_scale method or a scale property. Possibly the same for the "selected label".

Any thoughts? Am I missing something obvious? If not, does that sound like it would be a good addition?

[lcmcninch]

This issue was addressed in #42