Preliminary support for feature customization
Migrated to a pure GtkWindow
Remvoved expanders, instead use one checkbox to control the view of the "advanced mode"

Some other cosmetical changes
Padding is important.
Connect the checkboxes.
Single package removal is now working.
Don't try to be smart when removing single packages.
Added non-free support.
1.70.0
Ensure we mark for deletion the entire contents of the meta package(s)
1.90.0
Added oneslip feature.
Bugfix.
bricks can now prompt the user to install a missing feature.
Updated translations.
Catch KeyboardInterrups, fixed translations in error_label. We are 2.0.0 now.