Added work on integration of concurrency classic tests
added the VDMThread class to the runtime.
+change the appropriate transformation to extend the VDMThread class instead the native thread.
+update the test results.
Merge remote-tracking branch 'origin/gk/codegenconc' into pvj/main

Conflicts:
	core/codegen/src/test/java/org/overture/codegen/tests/utils/CompileTests.java
Added the POP3 model as a test (Test 1 in POP3Test)

The model is slightly changed to fit the testing system
Slight improvements to the testing system that executed the generated Java code

Large outputs are now limited to a fixed number of characters
Changed the way that the output of executing the generated Java code is read in the testing system.

Now the output is read using a separate thread.