Merge strain workchain and banddos workchain

[broeder-j]

These two are fairly similar and the strain workchain should be merged into the banddos workchain if possible.

The code of the strain workchain is rather old. But the strain is evaluated with a 3 point formula so currently only works with 3 points. This prob has to be generalized or a case build in that it is not calculated else. On the other side 3 points for a BM fit is not enough.