Base_getUpgradeBusinessTemplateList: Include core business templates.

Both so that changes to the list of core business templates are applied on
upgrade, and to avoid uninstalling core business templates, if no other
maintained-up-to-date business templates depend on them.
Also, improve the documentation of the erp5_upgrader version of this
script.

bt5/erp5_configurator_standard/SkinTemplateItem/portal_skins/erp5_configurator_officejs_sdk/TemplateTool_getOfficeJSDevelopmentBusinessTemplateList.py

@@ -5,7 +5,9 @@ keep_bt5_id_list = []
 
 bt5_update_catalog_list = ('erp5_ingestion_mysql_innodb_catalog', 'erp5_full_text_mroonga_catalog')
 
-bt5_installation_list = bt5_update_catalog_list + (
+bt5_installation_list = tuple(
+  context.getPortalObject().getCoreBusinessTemplateList(),
+) + bt5_update_catalog_list + (
   'erp5_configurator_standard',
   'erp5_upgrader_officejs_sdk',
   'erp5_administration',

bt5/erp5_upgrader/SkinTemplateItem/portal_skins/erp5_upgrader/Base_getUpgradeBusinessTemplateList.py

 """
-  This script should returns always two list of Business Template.
-   - The first list is to resolve dependencies and upgrade.
-   - The second list is what you want to keep. This is useful if we want to keep 
-   a old business template without updating it and without removing it
+This script may be overridden.
+It is expected to return two lists of Business Templates:
+- The first is a tuple containing names of Business Templates to install and
+  keep up-to-date. Their dependencies are also installed and kept up-to-date.
+- The second is a list containing names of Business Templates which should be
+  kept if already installed, ignored if missing, and not be upgraded nor
+  removed.
 """
-
-return ('erp5_base',), ["erp5_upgrader"]
+return (
+  tuple(context.getPortalObject().getCoreBusinessTemplateList() + ['erp5_base']),
+  ['erp5_upgrader'],
+)

bt5/erp5_upgrader_test/SkinTemplateItem/portal_skins/erp5_upgrader_test/Base_getUpgradeBusinessTemplateList.py

-return ('erp5_web',), ["erp5_upgrader", "erp5_upgrader_test"]
+return (
+  tuple(context.getPortalObject().getCoreBusinessTemplateList() + ['erp5_web']),
+  ["erp5_upgrader", "erp5_upgrader_test"],
+)