added a header file for typedefs and prototype definitions. Preparation for adding of unit tests.
added unit test framework (googletest) and target for unit tests dlt-sort-unittests
added first set of test case with 4 tests.
just moved parts into dlt_sort.cpp/h to enable unit tests with different project. no functional changes.
added one helper function. no functional change.
added some tests for class Lifecycle.
added one helper function. no functional changes.
some more tests
empty test functions for tests that need to be added (currently tests not implemented, reported as failing)