Fix CanvasFeatures histogram and feature hidpi rendering
Commit 1/3 - Add highdpi canvas, but change the width css by taking away the //c.style.width = oldWidth + 'px'; since it is percent based
Commit 2/3 - Fix height rendering on the highdpi canvas by making y-coordinates relative to the pixel ratio
Commit 3/3 - Fix the track layout by making the heightUpdate for the blockBased renderer relative to the pixel ratio
Update release notes for High DPI features
Merge branch 'master' of https://github.com/GMOD/jbrowse into clear_highlight_button
Beginning of Tristate Button
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
Add default dojo stylesheet for tristate checkbox (needs customization)
Add icons for the highlight buttons, however dijitButton stylings are lost
Remove old highlight code
Update to a new icon set specifically for the highlight button