feat: Added support for the BBOB's multi-modal functions with weak global structure

- Schwefel Function
- Gallagher’s Gaussian 101-me Peaks Function
- Gallagher’s Gaussian 21-hi Peaks Function
- Katsuura Function
- Lunacek bi-Rastrigin Function

Signed-off-by: Sebastian Niemann <niemann@sra.uni-hannover.de>
devel: Forced numbers to be of type double and set loop indecies to be unsigned

Signed-off-by: Sebastian Niemann <niemann@sra.uni-hannover.de>