allow for including redux in non isolation unit testing

[daithi-coombes]

This pr is to fix: cant run with phpunit: PHP Warning: headers already sent by (output started at bootstrap.php:53) pluggable.php on line 1196 .

I've found that the main issue that was causing my plugin unit tests to fail was the use of php setcookies() function writing headers(), to solve this I created a reduxCookie class that I could mock or overwrite in my unit tests.

I've also added the following to the pr:

• composer version number 8a94c53
• unit testing instructions in condributing.md cb7b9f2
• reduxCookie class 3193533

[kprovance]

Instead of adding a new file for the static setcookie function, I'm going to add it into our functions class instead. Plus, we're a few versions ahead of .1. I will credit you accordingly. :-)

[daithi-coombes]

@kprovance cheers ;)

if it helps - I think that build fail is from me checking the flag WP_TESTS_DOMAIN to prevent printing to stdout when running tests: here

[kprovance]

Added to upcoming push! ;-)