Refactor init shape matrices

Preparation for the follow-up MR (!3064 (merged)) extracting computeShapeFunctions() method for arbitrary points (not only integration method's points).

Refactoring consists of:

• small generalization of the initShapeFunctions() method
• moving it to NumLib (uses and depends only on NumLib/Fem)
• deduplicating code where the shape functions are computed for the given integration method.

Review commit-wise.