Move all subroutines in modules

If we move subroutines, such as WRAPUL, CGR, etc. into modules, we don't have to write explicit interfaces for those.

We can combine this with some additional refactoring:

• Rename files, such that all that define a module end again in "_mod.F90"
• Move all use statements at the beginning of modules.
• With the use statements, we can determine the interdependence of targets and write them out in the Makefiles.
• Put global private statement in each module. This will improve the encapsulation. It will, for example prevent the "inheritance" of use statements.
• Add attribute save to all module variable.