Clicking on math should select the clicked block

[acpiplica]

We want to support interaction where clicking on part of the math will select the term you clicked. A single click to select is applicable to selecting parts of static math when that math is presented prominently, like in MathJax's block display math. That's a fairly special case, though, and MathQuill doesn't distinguish between inline math and block math. Double-click to select is a more expected behavior in text editors/web pages and is already discussed in main MathQuill's Issue 127.