This allow filtering category item lists so that user can only select nodes /
leaves in a way similar to filter_{node,leave} but instead of removing the
items, keep them with None as relative URL. This is something Formulator
understand, categories are displayed with disable attribute set on the select
option, which allows to visualize the category hierarchical structure, while
not allowing user to select {nodes,leaves}

most trade and PDM report are about "what quantity of resources do we
have here", in most uses cases, we are not concerned about who is the
owner of these, so it's probably better to not select these by default.

For now only with "default purchase price"

Similar to Quantity Split Solver, but using FIFO delivery solver, so
that user does not have to choose a delivery solver.

a solver that can automatically accept all divergences, except on
quantity{,_unit}

In order to make solving divergences easier, we sometimes don't need to
show the delivery solver (priority) field when the solver only allow
one.

for now used in solver configuration only

Using an em html tag is enough to have to display the explanation
message differently, not need to wrap it in paranthesis, which does not
look so good in some languages.

Listbox supports setting '' (empty string) as an URL column to disable
the link, but None was never really supported, even though it worked in
the old UI.
When setting using the "key | value" form of formulator, if value is
empty, it's not None but an empty string. This is also what we test in
portal_tests/listbox_zuite/testUrlColumns

formulator passes arguments, no need to look in request by hand. Also
this makes scripts easier to test if passed arguments are used.

This is required to be able to use solve divergence action

When using checkPythonSourceCode integrated in the source code editor,
for a scenario where developer edit a component and save we can benefit
from caching the check message for the source code content, because the
same check that the one happening in the editor will happen when the
component is saved.

This cache varies on:
 - "component_packages" cache cookie which is reset every time some
component code is edited.
 - zope startup time to take into account editions of file system code.
This assumes that after reseting file system code zope will be
restarted.
 - portal_type, because the checks performed by this function also
depend on portal type.

this makes completions works when using Ctrl+space

This makes "Format Document" / "Format Selection" work.

because pylint is a bit slow on large components, debounce every 2
seconds. TODO: this is too slow.

For now this is just the portal_url, but I'm thinking it could be a
proper tool.