Prevent users from copying full fixed datasets and explain how to use them directly

[prioux]

This weekend a user couldn't figure out how to select a bunch of files from an installed dataset directly and instead proceeded to copy them all into their own private project.

This duplicated over 100GB of files.

The user wanted to select these data files alongside their own license file for a tool (that one in their own project) in order to launch that tool.

We need a better way to explain to users how to select files that are in different projects.

Also, we might want to prevent copying of files from fixed datasets. There is already a clumsy mechanism that limits what can be copied where (a DP can be set so that its files cannot be copied to other specific DPs) but this ties to some of the issues already in GitHub ( #1004 )

Also, the user attempted to upload their license file to the dataset DP (this was allowed because of #1399 )