Update README

Need JDK 7 now.  Tried to be less Mac specific.
Update Android Studio info to 1.0.0
Removed info about Maven and IntelliJ.
Rearranged some chapters and added more info on how to contribute.

Change-Id: Ib0200a84cb2be923d14fa1bc4da8f018fb1349ac
Merge "Update README"