[Packaging] Exclude symlinks in the source package from installation.

It seems that `setup.py` started complaining about the installation of
non-regular files.

They seem to be created later anyway (as directories rather than
symlinks), so no further action should be required (hopefully).

MANIFEST.in

@@ -5,3 +5,13 @@ include platypush/config/*.yaml
 include platypush/config/systemd/*
 global-include manifest.json
 global-include components.json.gz
+
+global-exclude __pycache__/*
+global-exclude *.pyc
+
+# Exclude symlinks to avoid issues with setuptools
+exclude platypush/backend/http/webapp/public/icons/openweathermap/black
+exclude platypush/backend/http/webapp/public/icons/openweathermap/white
+exclude platypush/backend/http/webapp/src/**
+exclude platypush/events
+exclude platypush/install/scripts/ubuntu