New approximation for KG method. Nonadditive kinetic energy modeled by
a local atomic potential. Regtests for the method and the generation of
the potential (atom code) added.


git-svn-id: svn://svn.code.sf.net/p/cp2k/code/trunk@13561 bac0169d-1eea-4375-b5f6-f89d2ced9994