Directory names conflicting with file names

[jo-pol]

What this PR does / why we need it:

Downloads result in unzip problems for datasets with full file-paths duplicating directories. Note that directory does not just mean the directoryLabel, but also the parents in the directoryLabel.

• EditDatafilesPage: message shows all conflicting files, not just the first
• a file with a directory conflicting with an existing full path is rejected
• files with a full path that conflicts with an existing directory will get a sequence number added
• additional unit test
• manual test script
• scripts to detect (latest version of) datasets with conflicting directory paths

Which issue(s) this PR closes:

• Closes #

Special notes for your reviewer:

Suggestions on how to test this:

• Adjust constants at the start of test-apis.py to meet your system and an empty dataset. Output with dashed lines show expectations after deploy. See also screenshots below.
• Download all files resulting from test-apis.py before this fix, unzip fails.
• Deploy the fix - try to add a non-conflicting file to the dataset with conflicts - saving the dataset fails
• Try to add files with files conflicting with existing directories to a healthy dataset: they will get a sequence number
• Try ta add a file with a (parent) directory that exists as a file: saving the dataset will fail.
• Adding files to a directory that already exists should succeed.

Does this PR introduce a user interface change? If mockups are available, please link/include them here:

See the changed dataset-management.rst file, the other changed rst file had a typo.

Is there a release notes update needed for this change?:

Existing datasets with the new type of duplicate names should be identified, see: scripts/issues/dirs-duplicating-files/find_duplicates.py The reported datasets should be fixed manually, best before deploying this fix. Depending on your preferences and the size of your database you might want a variation of the scripts.

Additional documentation:

Screenshots for the results of test-apis.py before and after deploy. Before depoly we see conflicts on foo and foo/bar), after deploy some request return 400-bad-request.