Added EnvVars hashmap if you have the EnvInject plugin

I noticed that getting the build's environment variables is tricky and is really catered towards parameterized builds. I added an optional dependency, the EnvInject plugin, that allows the user to grab any injected or environmental variable in the build. The user can access these from a HashMap "envVars" in the script much like how they access the badgeManager with the "manager" variable.