Add "All Groups" option.
Handle selection of all groups.
Handle selection of all users from All groups item.
Select all the groups.
Replace selection icons.
Replace selection icons.
Add option to toggle between user and group view.
Only use one type of menu.
Enabled or not the group submenu.
Remove group/user display menu.
Remove method displaying group menu.
Fix layout of menu items.
Replace text.
Use Pillow instead of PIL

PIL is unofficially not maintained anymore and its installation via pip 1.5 or
later now requires to pass --allow-external PIL --allow-unverified PIL
The proposal of this commit is to use Pillow as a replacement.
Replace PIL by Pillow in misc. logging output
Add separator to menu.
Remove selection of user in group display.
Review selection of users when switching between views.
ExporterI: set tile size for exported files to 128x128

This prevents the OME-TIFF writer from writing each row of pixels as a
separate strip, which should improve performance upon re-importing the
exported file.

See ticket #11850.
Switch reindexer to use slf4j.