add unit tests for examples

The examples in corsika/Examples should be unit-tested as well. To turn them into unit tests, the examples should not print the results, but assert on them. The executable can then be added as a test in CMakeLists.txt. For this to work, the -g flag needs always to be added for these executables (asserts are deactivated in release builds).

Adding -g which is generally a good idea for all executables that are run as tests.