* Properly override WebSite Document in erp5_web_shadir by creating a new
  version_priority.
* Keep Web{Section,Site}TraversalHook in Product/ERP5/Document as these are
  not ERP5 objects. Also, add `kept_for_backward_compatibility_only` to
  importLocalDocument() to handle pattern where the Document class has been
  migrated but some code remains.
* Move WebSection_get*PrecacheManifestList Python Script from bt5 not depending
  on erp5_web to erp5_web_renderjs as this is required by CodingStyleTest
  (WebSection being now in erp5_web).

Move BusinessProcess Document from erp5_trade to erp5_core as CompositionMixin
depends on it and this Mixin is used by several Documents in erp5_core.