Revert "Migrate as much as possible to pip and requirements.txt"

This reverts commit 982594a4a5.

lib/beetsplug/__init__.py

@@ -0,0 +1,19 @@
+# This file is part of beets.
+# Copyright 2013, Adrian Sampson.
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+#
+# The above copyright notice and this permission notice shall be
+# included in all copies or substantial portions of the Software.
+
+"""A namespace package for beets plugins."""
+
+# Make this a namespace package.
+from pkgutil import extend_path
+__path__ = extend_path(__path__, __name__)