making Group/User dropdown menu configurable, close #11120 (rebased onto dev_4_4)



This is the same as gh-1294 but rebased onto dev_4_4.

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This PR covers [ticket 11120](http://trac.openmicroscopy.org.uk/ome/ticket/11120).
Additional configuration allows to manipulate drop down menu, as shown on the picture
![firefoxscreensnapz004](https://f.cloud.github.com/assets/1065155/653887/7143601c-d4e8-11e2-86fd-238a54a7d70b.jpg).

`bin/omero config set omero.web.ui.menu.dropdown '{"LEADERS": "Owners", "COLLEAGUES": "Members", "ALL": "All members"}'`