Include arbitrary Actions and BuildParameters into the called Job.

Actions and BuildParameters can be added as additional parameters to the
build call.

Also added a convenience statement "withParam", which tries to map the
following statement to a BuildParameter (optionally with arguments).

Example: build("my-job", param1: "x", withParam.gitRevision)

Where git Revision is mapped to GitRevisionBuildParameters from
Git-Plugin.

This is especially useful to have the build-flow job as director, starting a whole chain of builds using the same revision.