Introduce unit tests

• Run unit tests in multisite mode as well
• Add badge to readme
• Abstract redirection functionality to make it testable

.gitlab-ci.yml

@@ -88,7 +88,7 @@ PHP7.3:
 
 PluginSVN:
   stage: deploy
-  image: containers.ethitter.com:443/docker/images/debian:wp-org-deploy
+  image: containers.ethitter.com:443/docker/wp-org-plugin-deploy:latest
   before_script:
     - curl -o ./bin/deploy.sh https://git-cdn.e15r.co/open-source/wp-org-plugin-deploy/raw/master/scripts/deploy.sh
     - chmod +x ./bin/deploy.sh