Merge pull request #10 from heroku/vendorjdk

Vendor JDK into 10% of New Apps
Reviewed by @ryanbrainard
Log beginning and end of java build. Fixes #12
Log flags with java_compile_end. #12
Pull down JDK installer from common. #13
:ghost: output removed. #13
Log new apps.
Detect version of java
Log new apps. #15
Add detect JDK back.
Remove download JDK flag
Get the default version if no version detected. Fixes #17
Migrate to system.properties.
Always include jdk on $PATH
Existing apps should not download the JDK.
New apps should get system properties file
"Choose a JDK" Readme Instructions
Overlay JDK
Merge pull request #20 from heroku/jdk-overlay

Overlay JDK
Always vendor the jdk