Added SVN logging observer.

It isn't triggered by anything yet. When the observer is called, it uses
Blinker to send out a signal for every [T12345] marker it sees in the
first line of each commit log. Those signals aren't connected to anything
yet.

NOTE: this requires the 'svn' Python module , which is a wrapper for the
'svn' commandline client. This client needs to be installed on our docker
when we deploy.

attract_server/attrs_extra.py

@@ -0,0 +1,17 @@
+"""Extra functionality for attrs."""
+
+import logging
+
+import attr
+
+
+def log(name):
+    """Returns a logger attr.ib
+
+    :param name: name to pass to logging.getLogger()
+    :rtype: attr.ib
+    """
+    return attr.ib(default=logging.getLogger(name),
+                   repr=False,
+                   hash=False,
+                   cmp=False)