[cwconfig] create a virtual "cubes" package _CubesImporter now handle import of "cubes" and return a virtual module so that "cubes" is always importable without having to create a __init__.py in CUBES_DIR and add CUBES_DIR/.. to sys.path. Drop custom code in setup.py used to create CUBES_DIR/__init__.py and drop now useless warning when cubicweb is installed in develop mode Update test_cubes_path() and ensure 'cubes.file' is not loaded before testing its import. This test seems to have mistakes because cubes are loaded automatically when discovering cw commands (cubes.<x>.ccplugin), not sure how this should be fixed definitely.

Change hooks control (deny_all_hooks_but / allow_all_hooks_but) to be more predictable Prior to this, if one execute code like: with cnx.hooks.deny_all_hooks_but('metadata'): with cnx.hooks.deny_all_hooks_but(): # mycode 'metadata' hooks will be activated anyway in the inner block, which is rather unexpected (of course in real life you only see the latest hooks control statement, the former being higher in the call stack). This is due to the underlying usage of old `enable_hook_categories` / `disable_hook_categories` methods, which were introduced much before the now official context manager based API (with `cnx.[deny|all]_all_hooks_but(...)`). To move on, this patch drop the two legacy methods, rename and privatize related internal state on the connection (`hooks_mode` becomes `_hooks_mode`, `disabled_hook_cats` and `enabled_hook_cats` become `_hooks_categories`) and reimplement the `_hooks_control` context manager to simply update them. See the added unit test for details.

[cwconfig] make appobjects_cubes_modnames() public The method is used in cubicweb.cwvreg without underscore and outside of the config class, so let's make this method public. Fix autoreload with twisted.