Updated README and mde icon/text/image displayed when all builds are green configurable

Hi There,

Love this app, we have been happily using it for a few weeks now but when we upgraded to Jenkins ver. 1.502 the changes to how it manages jsonp borked it.

I have updated the README to describe how to configure Jenkins ver. 1.502 and up
to work with Jenkins Radiator.

I have also made the little heart displayed when all builds are green configurable - we put or company logo up when all builds are green.

Cheers

Chris