Add support for basic auth to the Gradle Wrapper

- username and password can be specified as part of the url eg http://user:pass@server:port/distributions/gradle-x-bin.zip
- username and password can be specified in the users gradle.properties
  systemProp.gradle.wrapperUser=userid
  systemProp.gradle.wrapperPassword=password
- documentation updated to include help un using users gradle.properties with the wrapper
- Added biz.source_code.base64coder to wrapper (only changes where to fix checkstyle violations)