Add a Linter to the project

A Linter should be implemented for this project. Linting validates the source code against the style guide to ensure source code remains compliant. A CONTRIBUTING.md file should be added to the repository root directory in order to clarify the style guide expectations for contributions (among other things).

A task should be added to the build.xml file to execute the linter against existing source code.

Created by: pmpowers-usgs

Closing as part of milestone. See #153 (closed)