Build system updates
This MR improves the overall build system configuration and adds a simple test configuration.
- App executables are now part of the default target and depend on the
- Raise minimum required CMake version to v3.16, resolving #6 (closed).
- Add executing experiments at
experiments/hansbo_reproductionas system tests, see #2.
- List Python sources explicitly, resolving #5 (closed).
- Remove spurious global filesystem library link.