Simplified Build Process

I hope this is an acceptable pull request. It seems every other time I tried to build OkHttp it gave me some kind of maven error that took time to fix each time.  It could be my machines or something else.  But I thought it might be easier just to use the pre-compiled jar file that OkHttp provides.  It saves build time, and it makes updating to the latest versions much easier.

This update is going to be a pre-cursor to changes I am make for the PCL library to support progress streams as I was talking about on twitter.