Changeset [9b093cf073939c4d98005d8f0b15cfa4315c2069] by Colin

Add three state button (no styling) that has the behavior (1) when there is no highlight, state of button is false and toggling it turns to true so that the highlighting function of the mouse is enabled (2) once there is a highlight, 'mixed' state of the button is turned on (3) once the 'mixed' state of the button is clicked, the highlight is cleared
https://github.com/GMOD/jbrowse/commit/9b093cf073939c4d98005d8f0b15...