Simplifying config.h for easier call from different .cpp files

[AndunHH]

In order to apply the changes by @phillipthelen in #10:

• changing the static Key names to dynamic ones

  the following changes were made:

• Changing config.h from variables to only pre-processor macros which can be included into every .cpp file without "multiple variable declaration" errors
• modFunc stays a define and the selection of the modifier function is chosen during compilation