UPDATE: Add dune-gfe dependency | Bending-isometries | Microstructure-classes | Macroscopically-varying microstructure

Update:

• Add dune-gfe dependency in dune.module
• Add Code for Macro-problem (bending isometry minimization)
• Switch to Microstructure-classes (on the Python side) this enables a macroscopic dependence of the microstructure
• New VTK writing
• Add Unit Tests for both Micro-/ and Macro-Problem