cmake python and tutorials update

Folks, I did some updates and I want you to look at them and approve as you like:
- I put the "EnablePython" option to the main CMakeLists.txt to conditionally enable compiling of the python bindings. It in turns defines "ALPS_HAVE_PYTHON" which is used internally. The latter BTW be better dumped into a config file. 
- There was a bug `alpscore/python/src/import_numpy.cpp:13:10: fatal error: 'numpy/arrayobject.h' file not found`, caused by not finding numpy in standard locations. I fixed it by importing a FindNumpy module. 
- I put tutorials on a flag `EnableTutorials` but we better move them to at least a separate dir to make scripting transparent.

Also it seems to me, that python module has a bit different structure to the others. So if we ever decide to split tutorials (#52) this might be also done for python. The similar thing happened with boost in some of package managers - boost-python is shipped separately from the other parts of boost.