Clean /usr/local Git repository before calling brew doctor

When formulas are deleted by the bin/brew update operation, files remain
untracked in the main Git repository causing brew doctor to return a non-zero
error code. This commit fixes this by calling git clean -df post brew update.
Note this will potentially wipe out files not related to Homebrew and should
only be used in a testing environment.
Prune dead symlinks
Add a helper to import a fake single image file.
Avoid use of createImage and import_image in chgrp tests where they are not needed.
Avoid use of createImage in delete tests where it's not needed.
Define a testing mode to wrap Homebrew uninstallation and cleanup

This commit should allow people to keep on using this installation script. A
TESTING_MODE flag is defined conditionally to the presence of a JOB_NAME
variable by default (but can be overriden). The Homebrew/pip uninstallation
and cleanup operations as well as the PR merging step are only executed if
this flag is on.
Drop JOB_WS environment variable

Since 4.4.7, the python dependencies script is installed as part of the omero
formula. Dropping JOB_WS allows to use the OMERO-homebrew-install.sh script
without cloning the main repository.
Check delete rsp.constraints only if ERR. See #10889
'multi-image' and 'fileset' lowercase in UI
Delete MIF message more similar to chgrp MIF message
Fixed typo in name.
Remove fileset thumbs from right panel
Don't show green tick if delete Error. See #10900
Modify status label to use progress bar.
Use stringbuffer instead of String.
Modify layout and display of import process.
Remove checksum code
Remove unused import.
Modify display time.
Modify usage of result component.