Expose file annotation namespace in the clients (rebased onto develop)



This is the same as gh-1397 but rebased onto develop.

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As discussed in the Paris meeting, usage of namespace will grow soon and we may want to expose them to users.

This PR starts a first trivial implementation of this exposition in the context of the File annotations by
- adding "Namespace: " to the Info window in OMERO.insight
- adding "Namespace: " to the tooltip in OMERO.web