core: make some __init__.py namespaceable for qt for splitting repository

In setuptools, it's not possible to have an optional dependency
triggering what files are installed and how to build certain files, we
have to make 2 setup.py.
Unfortunately, having 2 setup.py files does possible in one repository.
So, we have to split the repository in 2.
After this point, the repository will fork. One repository will take only
qt stuff, and the other repository will contain browser framework, cli apps
and modules.

Qt apps are under the weboob.applications package though.
To have 2 pip packages shipping files in the same root
package (weboob.*), the package must be namespaced. This can be achieved
by tweaking all ancestor __init__.py files.