Pan/zoom improvements for mouse and touch users

[theacodes]

Pan/zoom is currently implemented in a way that favors touchpads on laptops, however, its behavior is less than ideal for mouse and touch users.

See related issues:

• #4
• #7
• #12

[indrora]

Adding a call-out on how to zoom would be the biggest for me.

As someone used to mapping software, I assumed zoom = wheel, pan = click+drag.

[sago35]

With #71, touch operations on Android and iPhone are now possible.

[wc7086]

Referring to the kicad schematic editor, press the scroll wheel or the right mouse button for dragging

[sago35]

#85 was created. This adds support for panning by mouse drag. Also, an option has been added to adapt the wheel behavior to KiCad.