Update java example
PHP buildpack guide
Update platform doc
Rewrite Add-on Credentials

Removed references to file name "creds.json"
Added section about SET_ENV_VARS
Rewrite Python Helloworld
Use new example apps
Add 'Helloworld in Silex' to PHP guides
Update ruby guides
Add notes for Django and Django migration guide
Update Java guides
Update Guides/PHP/Buildpack.md
Update PHP guides
Review - fix AWS S3 guide
Review - fix GWT guide
Review - fix Spring migration guide
Review - fix Application Servers guide
Review - fix Helloworld guide