* Create and validate standardized java source header

Update Checkstyle to validate all java source files have a standard
header. Remove FixLiscenseHeaders.java unit test as it duplicates
Checkstyle functionality. Standard header is block java comment, instead
of dangling Javadoc comment. Create standard header template
(HEADER_JAVA) in project root. Reference header template in
build.gradle. Update CONTRIBUTING.md to exact text of header template.

* Convert Licenses from dangling Javadoc to block comment

Standardize License based off of HEADER_JAVA file. All headers are block
Java comments.

* Restoring FixLicenseHeaders.java and updating CONTRIBUTING date

* Updated License dates to 2016

Several files had 2017 dates for License. Checkstyle now specifically
looks for 2016 date in License comments.

* Fix bad logic for header check in FixLicenseHeaders test