Allow canceling select-to-zoom interaction with right click

[axelboc]

Fix #1370 -- this is quite a neat interaction, actually.

Couple of notes:

• Pressing the context menu key on the keyboard also cancels the interaction.
• Firefox does not fire the contextmenu event at all when Shift is pressed. So with the proposed solution, a select-to-zoom interaction configured with the Shift modifier key cannot be cancelled with right click.

[loichuder]

Neat, indeed 👍

[axelboc]

Bug fix: 5da1e6a