Add option to toggle in-line edditing on/off in JsonEditor

Hi, I modified the jquery.jsoneditor.js script to optionally make the fields that display the JSON structure not-modifiable. Also I changed jsoneditor.js and jsoneditor.html to utilize this option.
It's a great addition if you wan't only to display a beautified JSON but not modify it.

It looks like this, not very distinguishable, but the input fields are disabled

![screenshot from 2014-05-12 16 05 45](https://cloud.githubusercontent.com/assets/4578022/2945205/c2108302-d9de-11e3-824a-07a2ceda6102.png)

Also changed the jQuery script from 1.6 to 2.1.1, jquery.jsoneditor.js was failing because of the .on method currently on line 53 in my branch

Cheers