move code from `Oscar.jl/experimental/GModule/Misc.jl` here

[ThomasBreuer]

The idea is to add this code to Hecke.jl, and then to remove it from Oscar.jl.

Once we agree what shall be really added here, tests and documentation has to be added. (I am quite sure that I have put certain parts into the wrong files, and that some functions have to be changed. For example:

• The function dual belongs to Hecke.jl, but the method in question deals with objects from AbstractAlgebra.jl; should dual better get defined in AbstractAlgebra.jl?
• pseudo_inv is defined in AbstractAlgebra.jl, the method in question uses MapFromFunc, which belongs to Hecke.jl; what is the relation between Hecke.jl's MapFromFunc and AbstractAlgebra.jl's FunctionalMap?)