Add missing FAIR data descriptors

[KRiedmiller]

The current training UI is missing some fields to create bioimageio models which fit their fair criteria:

• authors: free form
• cite: One citation should be panseg, others free form
• licence: dropdown with the option to not set any
• documentation: free form markdown
• input/output sample tensor: some bits of validation/training data?
• cover: could be autogenerated from test i/o

This would probably require a pop-up of some kind as the space is too limited.