started reworking the molecule class (not working yet)
added some data and functions to the molecule class
added some function prototypes to molecule class
added Doxygen style comments to the molecule methods
added three new classes for molecular groups

- abstractMoleculeGroup: abstract class which contains features
                         common to all molecular groups

- MoleculeGroup: general alignment of molecules without any
                 constraints on their orientation

- MoleculeStack: stacked alignment such that the molecule's least-
                 squares-planes are parallel
added the new grouping classes to namespace molconv
added a point between atoms to the list of internal origins
added an opaque pointer to class abstractMoleculeGroup
added the correct include directive of the base class
added some functions to molecule and modified the private molecule

added three more get-functions to the Molecule class related to the
internal origin/basis and added an initializer function to the
MoleculePrivate class.
renamed two member functions to fix overloading problem
implemented the function Molecule::internalOriginPosition()
started implementing the function Molecule::internalBasisVectors()
added function prototypes regarding the internal basis
added the previously declared functions to molecule.cpp
implemented some member functions of molecule
changed initialize function to be the constructor
implemented two more member functions of Molecule
implemented functions calculating eigenvalues/-vectors
implemented member function setOrigin()