Auto-load commonly used modules in manage.py shell.

This automatically loads settings, zerver.models.* and
zerver.lib.actions.* when you start `manage.py shell`, which should
save a bit of time basically every time someone uses it.

Fixes #275.

scripts/lib/pythonrc.py

@@ -0,0 +1,11 @@
+from __future__ import print_function
+try:
+    from django.conf import settings
+    from zerver.models import *
+    from zerver.lib.actions import *
+except Exception:
+    import traceback
+    print("\nException importing Zulip core modules on startup!")
+    traceback.print_exc()
+else:
+    print("\nSuccessfully imported Zulip settings, models, and actions functions.")