Separate config specific directory for python builds

[ptheywood]

The swig/python output files are not config aware, i.e. a Release and Debug build in the same build directory will overwrite one another.

It should probably go into lib/<os>/<config>/python/.

<os> is not strictly required, as we do not track the build directory and do not support cross-compilation, it is mostly just a FLAME GPU 1 legacy thing. We could remove it but it also isn't causing any harm.

Currently, the build/lib directory on linux after a Release build and a reconfigure to a debug build is looks as follows (directories, 4 layers deep):

tree -d -L 4 lib/
lib/
└── linux-x64
    ├── Debug
    ├── python
    │   ├── build
    │   │   ├── bdist.linux-x86_64
    │   │   └── lib
    │   ├── dist
    │   ├── pyflamegpu
    │   ├── pyflamegpu.egg-info
    │   └── venv
    │       ├── bin
    │       ├── include
    │       ├── lib
    │       ├── lib64 -> lib
    │       └── share
    └── Release

This can probably just be addressed when the swig cmake is adapted to create several swig/python modules to support namespacing.

It might be worth considering moving the swig/python bindings out of lib, as they don't really belong there (i.e. it's not a .so/.lib file). Perhaps build/python/ or build/pyflamegpu? (although need to be careful with directories that swig will already create due to target names / subdirectories that have been added, i.e. build/swig/python already exists.