Added and refactored Brayns plugins

[favreau]

The following plugins are impacted by this PR:

• brayns-atomic-volumes
• brayns-circuit-explorer
• brayns-dicom
• brayns-diffusion-tensor-imaging
• brayns-fractals
• brayns-graphs
• brayns-membraneless-organelles
• brayns-molecular-systems
• brayns-morphology-synthesis
• brayns-steps
• brayns-brain-atlas
• brayns-topology-viewer