[repository] Drop the entities.extid column and associated cache This was not necessary anymore with promoted usage of the new data import API. Turn repository's _type_extid_cache to _type_cache with only the entity's type as key. This introduces an backward incompatible change: entity_metas dict doesn't contains anymore the extid key, but it doesn't seem used at all anywhere, so this sounds acceptable. Closes #15538317

Web side development
====================

In this chapter, we will describe the core APIs for web development in
the *CubicWeb* framework.

.. toctree::
   :maxdepth: 2

   publisher
   controllers
   request
   searchbar
   views/index
   rtags
   ajax
   js
   css
   edition/index
   facets
   internationalization
   property
   httpcaching
   resource