This will not work when there are several nodes anyway, so just display a
message to the user instead.

Also, upon installation of bt5s, install WorkflowItem before Components as it
is needed to restore history.

Another solution would have been to validate() ZODB Components automatically
upon bt5 installation but it would mean losing 'modified' state information
and also imply that *all of them* will be validated even if a developer wants
to publish non-validated ZODB Components.

getattr() will never load the Component, whereas import does. Also, unit tests
were passing with this bug, so improve unit test so that asserting that a
module is importable does not have side-effects.

For now, just ignore it but it may be required later to define dummy accessors
so that the registry and Components can be loaded even when their accessors
are not generated yet.

It is exactly the same at the end but the name of the latter does not make
sense in this context. Moreover, it allows to get rid of Base import.

Make tab's right image longer so when used as background we don't see a missing border above gadget's title.

Adjust background images' color which was different one than default one and make a visual difference.

Fix "Modified wf condition to get transitions to be available even if causality state is in "draft""

- Now when a delivery is cloned and since Julien commit 5c09e2, scripts are no longer called to "start_building" and  "update_causality_state", the delivery therefore remains in draft state. Transitions that were waiting for the the delivery to be in a "solved" state were not available any longer.

this was actually "dry run"

Also minor fixes on comments and make a set of base categories for faster
lookups

* no limit instead of 1 by default.
* no listbox rendering until the dialog is updated so that we get the dialog quickly.

Supply Lines from trade conditions should not be applicable once the trade condition is invalidated / deleted

pyPdf goes in an infinite loop when PdfFileReader are created on an empty file.