Merge pull request #1239 from sbesson/rebased/develop/virtualbox_omero_version

Use omero.version to generate the ova name (rebased onto develop)
Blitz getThumbnail(direct=True) uses direct methods by default
webgateway render_thumbnail() uses img.getThumbnail(direct=False)
Fix cached thumbs bug in SPW. See #10827
Adding git user config for travis
Replacing number-dash with double dash
Fix issue if log file is the only file submitted.
Merge pull request #1221 from will-moore/split_MIF_warnings

Split mif warnings
Provide SYSTEM priority thread executor for reload (See #11033)

Along with the other resource contention issues seen under 11033,
a number of imports performing stats calculation led to SM.reload()
blocking. Since this is called by getEventContext() all of the
joinSessions from OMERO.web were blocked, completely breaking the
client.

Now, a special `ExecutorService` is available for high-priority
threads. It will grow without bound, but threads will be cached
and reaped as necessary. A better implementation might try to
use a single thread pool, but save a few slots of system threads.
Merge pull request #1236 from jburel/import-bugs

Import bugs
Merge pull request #1242 from jburel/multi-selection

Fix multi-selection in data manager (see #11037)
Fix DummyExecutor
Splitting travis task into environments
Fix indent.
Fix typo.
Adding build-default to test env
Use Enum as suggested by Mark
Remove code commented out prior to this PR.

No need to keep it.
Fix text after cut and paste.
Remove unused import.