image popup: zoom, pan, scroll
目前为
// 1. to use hover over the image(container) to view a popup of the target image
// 2. to zoom in/out use wheel up/down. to reset press the scroll button
// 3. click left mouse to lock popup this will make it move along with the mouse, click again to release (indicated by green border)
// 4. while being locked the wheel up/down will act as scroll up/down
// 5. double click will lock it on screen preventing it from being hidden
// 6. while locked at screen (indicated by red outline) a single click with the blurred background will unblur it, only one popup per time, so the locked popup will prevent other popup to spawn
// 7. double clicking on blurred background will de-spawn popup
// 8. to turn on/off hover at the bottom of the page
