Convert GBW to WFN

[ezpzbz]

In order to use the results to perform QTAIM analysis, we need to convert gbw to wfn or wfx file.
There are two possibilities here:

• Doing it at plugin level: it means that we can define a new calculation class which takes the gbw and applies the conversion.
• Doing it at workchain level: we can define the simple calculation as a calcfuntion.