Add Fuzzy Segmentation Based Volume Creation

[faberno]

• added fuzzy case to SegmentationBasedAdapter (+activated gpu)]
• adapted segmentation_loader example
• refactored assert_equal_shapes test

Please check the following before creating the pull request (PR):

• [ ] Did you run automatic tests?
• [ ] Did you run manual tests?
• [ ] Is the code provided in the PR still backwards compatible to previous SIMPA versions?

List any specific code review questions

• how to handle "seg" field for multiple classes per voxels?

Provide issue / feature request fixed by this PR

Fixes #399