fix #9961: interactive dialog before overwriting a local file (rebased onto develop)



This is the same as gh-1455 but rebased onto develop.

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Fixes https://trac.openmicroscopy.org.uk/ome/ticket/9961 -- when trying to save a file annotation locally, if you would save on top of an existing local file then you should get a decent overwrite / change name dialog option, and it should all work properly.