Use setuptools entry_point instead of namespace

Requires poezio update (3577f887).

This simplifies some things for the tooling. No more name conflicts with
the omemo library for one, and no need for an almost empty folder.
Signed-off-by: Maxime “pep” Buquet <pep@bouah.net>

setup.py

@@ -16,7 +16,7 @@ from setuptools import setup
 
 MODULE_FILE_PATH = os.path.join(
     os.path.dirname(os.path.abspath(__file__)),
-    'poezio_plugins/omemo', 'version.py'
+    'poezio_omemo', 'version.py'
 )
 
 def get_version() -> str:
@@ -59,7 +59,8 @@ setup(
     url='https://lab.louiz.org/poezio/poezio-omemo',
     license='GPLv3',
     platforms=['any'],
-    packages=['poezio_plugins.omemo'],
+    packages=['poezio_omemo'],
+    entry_points={'poezio_plugins': 'omemo = poezio_omemo'},
     install_requires=['poezio', 'slixmpp-omemo'],
     classifiers=CLASSIFIERS,
 )