Canvas rotation easy to accidentally change

On 1.0alpha (ca4cbd5, Mac, 2019-05-29) -- Also observed on Windows.

The lower-right hand corner of the screen, where one grabs the corner to resize the window, is filled with the canvas rotation button. It is a bit tricky to resize the window without accidentally rotating the window. Since it has happened to me quite a few times, I imagine that it will happen to new users much more often.

The issue is exacerbated because (A) a user may not know what has happened and why the image is rotated, and (B)( there is no way to undo a canvas rotation.

In prior versions (0.9x and earlier), the control did not quite go all the way to the corner, so the resize target was larger.

Some possible solutions:

• Reduce the size of the buttons
• Add an inactive border around the buttons
• Add a little space to the right of the buttons
• Add a "resize" UI indicator to the right of the buttons.