* Added CommandFactory and a ServiceLoader model for providing
implementations
* Added ScriptCommand (wrapping groovy script). Service providers
are recommended to implement OptionHandler in their script, but a
regulare Script or a Runnable will also work.
[#50427095]
* Because Spring is not on the classpath we don't particularly
want to use SpringFactoriesLoader
* Adopted the JDK (>=6) ServiceLoader model instead
[Fixes#48789783]