Get Reply button as clicked target in notes.js.coffee

See issue #401 (closed)

This is a small fix to properly find the reply button as the click target when an element inside the button is clicked (e.g. in this case, the <i class="icon-comment"> element in the button, using the jQuery .closest(...) function.

Previously, the clicked element was assumed to be the button itself, which caused the comment form to spawn within the button when it was clicked (see the issue for screenshots & other details).