Migrate to WP CLI and PHPUnit based Unit Tests

[mtekk]

Rather than the current set of internal unit tests that can't be easily distributed, a new set using PHPUnit and WP CLI needs to be build and shipped with the plugin. See http://wp-cli.org/blog/plugin-unit-tests.html

[mtekk]

Unfortunately, the groundwork for this will be all that gets into 5.1.0. Punting to 5.2.0

[mtekk]

This will be an ongoing effort, not a blocking/blessed objective for 5.2

[mtekk]

This will be a long term thing, but the infrastructure is now setup to start doing this

[mtekk]

As of now the uninstaller and the bcn_breadcrumb class have tests. Need to add tests for the filters in bcn_breadcrumb. Then, it's off to implementing tests for bcn_breadcrumb_trail. adminKit and the admin stuff with nonces will be the most difficult to write tests for due to having to deal with the nonces. This is a good enough of a start for 5.3.0, will move the issue to 5.4.0.

[mtekk]

Calling this good for 5.4, bumping it to the next release as it's an ongoing effort.

[mtekk]

Calling this good for 5.5, bumping it to the next release as it's an ongoing effort.

[mtekk]

We're good for 5.6, bumping it to the next release as it's an ongoing effort.

[mtekk]

Just migrated to using Yoast\PHPUnit-Polyfills to avoid some silly PHPUnit API craziness