Add support for loading script from file/classpath in the language component in camel-core

See forum
http://fusesource.com/forums/thread.jspa?messageID=12388&#12388

We should add support so people can specify

language:groovy:classpath:com/mycompany/mygroovy.groovy

As well as use file paths

language:groovy:file:etc/mygroovy.groovy

eg file: and classpath: is prefixes for loading resources.

Likewise the header (CamelLanguageScript) should support this as well