Logger loader

This is an old piece of code that I am migrating toward SWIFT. I just want to use gitlab to review this by myself first.

I have written a library that reads the logger data. It is still an early implementation that works but could be improved a lot (new features and some optimizations). Currently only a serial version exists.

You will need python and the logger to use this code (./configure --enable-logger --disable-mpi --with-python=/usr/). The logger works only with the Gadget SPH (without gravity and stars). My main test consists in running the SedovBlast_3D.