Martini CG - Combined angle-torsion potentials

- Potential important for Martini
- Most Important diffence: bondfree.c
- Rest of files: definition of types
- Different MD groups want to have it
- Avoid the numerical instabilities
of having three beads in a row and
therefore an undefined dihedral
angle. This might not happen easily
at the atomistic level, but for coarse-grain
models this is a real pain.
- Paper at
http://md.chem.rug.nl/~monica/Bulacu_Marrink_2013.pdf

Adopted new tpx_version scheme.

Paper published.
Change-Id: I8ed470c464d843eb0218c87aeea3a44c3a1f64f8