Fix Warnings

We still get many warnings if you enable ELSA_BUILD_WITH_MORE_WARNINGS. We should fix start fixing them.

Modules:

• core
• functionals
• generators
• io
• logging
• operators
• problems
• projectors
• projectors_cuda
• solvers

Other TODOS:

• Enable ELSA_BUILD_WITH_MORE_WARNINGS for pipelines

Do we want any more warnings? Any specific useful warnings we should turn on? Do we want one common branch, or should we go with multiple ones?

@all feel free to contribute :-D