Fix #562 enhance zoom origin behavior when using icons in the control bar to zoom image

[SusieWen777]

This allows the zoom origin to behave as the follows when using icons in the control bar to zoom image:

• If the image has been clicked by the mouse or been touched, the zoom origin will be the last place of the mouse or the touch point.
• Otherwise, the zoom origin will be the center of the image.

Summary

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• Bugfix
• Feature
• Code style update
• Refactor
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• No

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The PR fulfills these requirements:

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Other information:

[fengyuanchen]

Don't add auto-generated files (dist/* and docs/js/viewer.js).