PNGs instead of PDF

First idea: Using PNGs on the iPad app instead..
Merge branch 'master' of https://github.com/yannickulrich/presenter

Conflicts:
	ipad.js
	ipad.php

Ok, I made stuff working via PNGs (the old code is still there but commented)
 - I used this pretty cool library to handle the drawing: http://ianli.com/sketchpad/
 - The slides on the iPad are just background-images of the drawing 'canvas' div
 - the news.php is now called get.php following Issue #3
 - The get.php has a new option: images It returns a list of image urls for the slides. They're still static - and yes, I filed an issue
 - The iPad interface got two new buttons: Eraser & Pen
 - The App has an ENUM to identify the tools

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