Zoom behaviors during video annotation

[sbatchelder]

When during video annotation, and particularly using FrameSeek: Auto, the zoom controls are not intuitive. Here are some additional zoom behaviors that would enhance user experience.

• Zoom resets when localization changes. This should be the default behavior when changing frames too, and the behavior should be toggleable for backward compatability
• Zoom changes to focus on localization when localization changes and FrameSeek + ZoomAutofocus (new interface toggle) is enabled. This should maintain 1-to-1 aspect ratio
• Zooming with the scroll-wheel. when the mouse is on the frame canvas. Use the scroll-wheel to zoom in/out and maintain 1-to-1 aspect ratio, even when Zoom Tool on the left is not selected. The zoom buttons on the left should only be used for custom non-1-to-1 box selection. Reset zoom using mouse middle-click.

[jrtcppv]

This is aligned with feedback we have received from other users. We will plan on implementing it after 0.2.19 is released.