Fixed two small bugs in input generation

In generate.sh, the inputgenerator.py is now called as a local script.

In inputgenerator.py, use /usr/bin/env to be independent of actual python installation dir.
Explicitly use python2, which is needed by the skript and not always the default anymore.

source/KKRnano/source/datastructures/generate.sh

 #!/bin/bash
 #inputgenerator.py Dimensions dimensions.txt > Dimensions_mod.f90
 cp InputParams_mod.F90 InputParams_mod.F90.bak
-inputgenerator.py InputParams InputParamsNew.txt > InputParams_mod.F90
+./inputgenerator.py InputParams InputParamsNew.txt > InputParams_mod.F90

source/KKRnano/source/datastructures/inputgenerator.py

-#!/usr/bin/python
+#!/usr/bin/env python2
 
 """
 Reads file defs.txt and generates Fortran code for reading an inputfile.