Deprecate everything in compat.catlib and compat.userlib

Id est:
* compat.catlib.Category
* compat.catlib.change_category()
* compat.userlib.User

The 'compat' submodule was never meant for direct use, but
a real deprecation notice has never been added.
Since replacing them with their 'core' equivalents is a
no-brainer, they will be removed quite soon.

Change-Id: Iaa29035d8f645724c4a5d09d90e64e03f2823f9a
Merge "Deprecate everything in compat.catlib and compat.userlib"