Resolve "unique ID for datafile and dataset" + Remove data management in admin view + data manager func

Closes #97

See merge request !44

Resolve "Expose unique ID for files"

Closes #61 and #60

See merge request !43

Resolve "Enable creation of empty datasets"

Closes #94

See merge request !42

for datafile

hashed files

uploaded. Don't delete file on disc unless it is the only DataFile pointing to
it.