Provide an import summary (see #12506).

This PR is an initial attempt at fixing http://trac.openmicroscopy.org.uk/ome/ticket/12506. It adds a summary line after the CLI import finishes. The output should be self-descriptive.

To test:
- do a CLI import of single-image/MIF datasets/folders and verify that the numbers make sense,
- import a broken image/log file (e.g. from `test_images_broken`) together with a valid image and check the error count,
- import a SPW file structure and check that the plate count is reported correctly.
Also check that tests in http://ci.openmicroscopy.org/view/5.1/job/OMERO-5.1-merge-integration-python/lastCompletedBuild/testReport/test.integration.clitest.test_import/TestImport/ are green (ones that have `Summary` in their name).

--no-rebase