UMLTP2 — ProcedureInvocation should specialize AtomicProceduralElement

The stereotype ProcedureInvocation allows fro invoking test-specific procedures such as TestExecutionSchedules, TestCases and TestProcedures, but also simple libraries.

It is currently specializes CompoundProceduralElement, which seems to be erroneous. The invokation of a test-specific procedure is an atomic instruction, and as such, it should specialize AtomicProceduraleElement instead.

The corresponding ProcedureInvocationArbitrationSpecification specializes AtomicProceduralElementArbitrationSpecification, though. So, what ever decision will be made with respect to ProcedureInvocation, the corresponding arbitration specification might require some re-work, too.

Change ProcedureInvocation to specialize AtomicProceduralElement instead

The FTF decided that ProcedureInvocation is not a CompoundProceduralElement, but an AtomicProceduralElement. This is already reflected in the editorial parts of the specification (i.e., the conceptual model and the arbitration specification section of clause 8), but was obviously incorrectly stated in the diagrams of both the conceptual model and the profile specification (maybe as a relic from the initial submission).

This issues will be resolved together with proposal #54 for issue #24