Decouple components

[havogt]

• moved components into sub-folders: serialbox, serialbox-c, serialbox-fortran, serialbox-python
• serialbox core builds, but needs cleanup and proper export
• serialbox-c build runs by doing a add_subdirectory on the core. this needs cleanup. and export
• serialbox-fortran and serialbox-python no work done.
• probably we should have a root cmake which installs everything as it does currently (if the compilers are compatible)
• see also Decouple building of core and bindings #207
• maybe serialbox core and c part should still be one project?