These tests were time-dependent and would start failing in 2018
when the golden files still have the copyright year of 2017.
Fix by hard-coding the year 2017 for the purpose of these two tests
to ensure reproducible builds.
Fixes#503
* Refactoring code that unnecessarily declares a map before making it.
* Cleaning up gpl3 formatting to match other licenses.
* Adding functionality that allows specifying custom license header
and text in cobra config.
* Using license header and text as templates so that they can use
template variables (for custom and gpl3 licenses).
* Adding ability to specify no license.
* Adding custom license example to README.
