Register OFS as a package and give it an initialize function. Moved registration of OFS classes there from Products.OFSP.

No longer create an `Extensions` folder in the standard instance skeleton. External methods will become entirely optional in Zope 2.14.

Factored out the `Products.ZSQLMethod` into its own distribution. The distribution also includes the `Shared.DC.ZRDB` code.

Removed fallback code for old `ZCatalog.catalog_object` function signatures from `Products.ZCatalog.ZCatalog.reindexIndex`.