Allow font family to flow naturally from surroundings

[danielbprice]

This component imposes a font selection as follows:

const initialBackgroundAndFontStyle = {
  backgroundColor: this.background,
  font: `${Math.floor(this.size / 2.5)}px/${this.size}px Helvetica, Arial, sans-serif`,
  color: this.fontColor
}

It's certainly possibly to use styles to override that, but it seems inconvenient; usually a component with text in it would naturally match the fonts of the things around it.

It seems like simply changing this to not select a font would be a more hands-off and natural approach.