MOLE v2.0.0 Development: Adopt new CPP software organization into the directory structure

Creating a new directory structure for the MOLE C++ implementation, as shown in Figure 1.

**Keep-open request**
- [x] I am requesting maintainer review for `keep-open`.

Reason:
Previous versions of MOLE had a directory structure that kept the C++ and Octave versions sharing subdirectories (i.e., src/cpp and src/octave). For MOLE 2.0, every programming language implementation has a different and independent subdirectory under the MOLE's root directory.