* 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).

/reviewed-on !521

Ensure that the data format returned is stable.
By default, imit the number of documents returned by the search.
Do not return document properties outside the form rendering.
Minor bug fixes.