Added INLINE_EDITING_ENABLED setting

Hi Stephen. The frontend editor is great, but sometimes gets in the way of specific/odd JS or CSS or can be confusing for some users. I saw there was some interest in being able to disable it easily, so I wrote up this patch. I think I covered everything, except for generating the new settings docs as I'm not sure about your process for that. Let me know if there's anything else it needs.

Thanks,
Jeff