Limitations update for 5.0.2 (rebased onto develop)



This is the same as gh-789 but rebased onto develop.

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See https://trello.com/c/ddAkwXxm/37-testing-plan-for-5-0-2-release - adding limitations noted from testing.

See https://www.openmicroscopy.org/site/support/omero5-staging/sysadmins/limitations.html to review