#1398 Change teat utility used from Catch2 to Boost.Test.
The reason for the change was partly bug #1363: tests were failing for macOS / shared library / release mode solely due to an internal error of Catch2. Now we need to have Boost Test installed (as usual ThirdPartyCompilationLibrary facility provides it). I also used the modifications to refresh the way tests were written: - Fixture are now handled in a much better way; in peculiar some tests no longer required a fake model and its equally fake Lua file to proceed. - The model tests have been refined to provide more information in case of failure (the complete path of the files that might not be equal are now directly given). - Mpi fixture is now working completely: you may define several test suites in an executable without having it fail (previously it was the case only for the full-fledged model fixture). This commit is unusually big for me, but that is due to the fact with macro everywhere in both Boost.Test and Catch2 I had rather not used them at the same time.