Compute vibration intensities for VASP format

The vibration intensities are not explicitely present in VASP output but
can be computed from the changes of dipole moments and the normal
coordinates.

Christian Neiss (FAU Erlangen Nürnberg) wrote the Python script that
served as the basis for this patch.
remove asserts
Merge pull request #104 from Synss/vasp-intensities

Compute vibration intensities for VASP format