Optimize x struct fields. Proposed fields:

• x.opts or x.settings: ExploreASL arguments and derivatives
• x.data: dataset specific fields
• x.vis: colormaps etc.
• x.tools: toolbox specific fields
• x.atlas: atlas specific fields
• x.study: study specific fields
• x.module.(structural/asl/population)
• ...

Add description for each field to documentation website

Edit 28.05.2021: The fields I started with are...

• x.opts (input arguments and their derivatives)
• x.dir (directories)
• x.settings (mostly booleans for pipeline settings and some other stuff)
• x.dataset (dataset related fields)
• x.tools (right now there's not much in there besides the spm version)