Add group and test method execution doc (see #11677) (rebased onto dev_4_4)



This is the same as gh-569 but rebased onto dev_4_4.

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This PR expands the testing document with help regarding running specific test groups and test methods (mainly in ``OmeroJava``). It also moves around the Eclipse paragraph and puts it closer to the Java test-writing text.

This should be safe to rebase onto ``dev_4_4``.