LPS-46696 - Prevent unintentional portlet dragging on mobile devices

Hi Jon,

Attached is another update for https://issues.liferay.com/browse/LPS-46696.

Based on @natecavanaugh's recommendations in https://github.com/natecavanaugh/liferay-portal/pull/2441, I was able to make several improvements.  The css selectors are much simpler and use the ```.portlet-title-text:before``` selector for the move icon (using the font-awesome mixin).  But I was unable to use that ```:before``` selector for the actual drag handle.  So unfortunately layout.js still has to touch the DOM to append an invisible span each portlet's handle :(.

I have also been working on a solution that would only use the ```clickPixelThresh``` and ```clickTimeThresh``` drag properties to fix the issue, but those don't seem to work as intended on touch devices.  I will continue to try and figure those out though.

Please let me know if there are any issues.

Thanks!