Add some CMake code to get boost::python in the build.

Needs some work most likely.
Add directives to locate python, add library and headers to build. Make python interface optional, but on by default.
Can build boost::python on Windows, it seems.
Taking Ayla's change
This part fails on my machine, even though the file is obviously there.
Need this on Windows too.
Switch to SCI python (git) repository.