CI build for binary wheels

[mirhahn]

Adds a manually triggered Gitlab action that builds binary wheels suitable for upload to a Python package repository. It uses the cibuildwheel tool to cross-compile wheels for a variety of platforms.

Remaining issues:

• Due to test_check_binary_solution fails on emulated ARM64 systems #34, disabling the test_check_binary_solution is currently required.
• Cross-compilation on Linux makes use of CPU emulation and takes a very long time (approximately three quarters of an hour on my test system) and can take much longer if there are configurations where no NumPy binaries exist.
• If any tests fail on any build architecture, cibuildwheel will discard all compiled binaries. This is currently unavoidable and appears to be an intended feature of cibuildwheel.