fix: prevent zoom on mobile when handleTouch is set to false

[sherwinski]

It appears that touchstart events on mobile will also trigger a mouseenter event by default, which will still create a ZoomPane element even if handleTouch is set to false at instantiation. This PR will prevent that default behavior in scenarios where handleTouch is set to false.
Fixes #273

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Steps to Test
Behavior on base branch: https://codepen.io/billythekid/pen/WqZwmW
Behavior on this PR: https://codepen.io/sherwinski/pen/GbbGYP

1. Open codepen link in Chrome browser
2. Open devtools panel
3. On the top toolbar, select "Toggle Device Toolbar" (cmd + shift + M) and using the drop down that usually reads "Responsive", select a touch device
4. Under the "Sources" tab, find the section called "Event Listener Breakpoints"
5. Checkoff the checkboxes for "mouse" and "touch"
6. Using the mouse, click on the image in the codepen
7. Step through each of the events trigger

In the base branch, a click will result in a "touchstart" and then a "mouseenter" event, whereas in the PR version only "touchstart" will execute.

[sherwinski]

Hey @billythekid, care to take a look at this and see what you think? I'm hoping this will solve the touch bug we discussed a few weeks ago.

[billythekid]

Heya @sherwinski,

This appear to work well, on chrome devtools 'touch mode', firefox devtools 'touch mode' as well as chrome on iphone so I'm saying this is a good catch and a nice way to do it actually, just unbind the event.

Thanks for checking it out!