mxp: Isolated environment

[kiesel]

The maven plugin uses preinstalled XP Framework runners. When just run w/o arguments they'll pick up the XP Framework installation configured for the user.

Applications should be able to define the XP Framework version they require, eg. when they use specific version-dependent features. In that case, the "default" framework should not be part of the classpath.

Of course, we'd first have to provide a maven build of the framework:)