401. Plugin infrastructure

* implements installing, loading and setup for plugins
* codifies configuration
* has a sample plugin
* docs
* tests

mediagoblin/plugins/sampleplugin/README

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+========
+ README
+========
+
+This is a sample plugin. It does nothing interesting other than show
+one way to structure a MediaGoblin plugin.

mediagoblin/plugins/sampleplugin/__init__.py

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+# GNU MediaGoblin -- federated, autonomous media hosting
+# Copyright (C) 2011, 2012 MediaGoblin contributors.  See AUTHORS.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+
+# This imports the module that has the Plugin subclass in it which
+# causes that module to get imported and that class to get registered.
+import mediagoblin.plugins.sampleplugin.main

mediagoblin/plugins/sampleplugin/main.py

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+# GNU MediaGoblin -- federated, autonomous media hosting
+# Copyright (C) 2011, 2012 MediaGoblin contributors.  See AUTHORS.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import logging
+from mediagoblin.tools.pluginapi import Plugin, get_config
+
+
+_log = logging.getLogger(__name__)
+
+
+class SamplePlugin(Plugin):
+    """
+    This is a sample plugin class. It automatically registers itself
+    with mediagoblin when this module is imported.
+
+    The setup_plugin method prints configuration for this plugin if
+    it exists.
+    """
+    def __init__(self):
+        self._setup_plugin_called = 0
+
+    def setup_plugin(self):
+        _log.info('Sample plugin set up!')
+        config = get_config('mediagoblin.plugins.sampleplugin')
+        if config:
+            _log.info('%r' % config)
+        else:
+            _log.info('There is no configuration set.')
+        self._setup_plugin_called += 1