Adding optional config to secure console execution

In some scenarios it is desirable to restrict access to the groovy console outside of JCR permissions. Added optional configuration labeled "Allowed Group" which, when specified, will have the only users allowed to run the console. When the config is not specified, the script is allowed to be executed.
Refactor permission code
Merge branch 'develop' of https://github.com/Velir/cq-groovy-console into Velir-develop
adding permissions check for configured groups and removed geb tests.