Fix for issue #1190

removed screenToTextBlockCoordinates from emacs.js. 

I have to confess I did not spend a lot of time trying to figure out what this function is supposed to do or why it is malfunctioning, but I had a hunch it was causing the problem, noticed that there is no similar function in vim mode, and just tried removing it. It fixed the problem.

In order to reproduce the problem and verify the fix, I added a keyboard selection button to the textarea bookmarklet. Use it to replace a textarea, say on http://www.echoecho.com/htmlforms08.htm
and switch the keyboard to emacs. On that site, (without my fix), no matter where you click in the textarea, the cursor stays in the top left corner of the editor. 

Previously emacs-mode was working OK with kitchen-sink.html, which positions the document absolutely at document position 0, 0. I verified that this still works.