Removed explicit dependency to logging plugin

 - resubmitted patch originally by fterrier. See
https://github.com/Grailsrocks/grails-cache-headers/pull/1/commits
Merge pull request #1 from robertoschwald/master

Removed explicit dependency to logging plugin so people can change the logging framework
update to latest version of Grails, fix metadata
Create README.md
ConfigurationHolder is deprecated - supress warning message