Commits correction framework is implemented

* Introduced new parameter in config file
* Added a notice for changed commits to UI
Also:
* Fixed default config param for sources_root
* Removed background image from layout

Implements blueprint commits-corrections-framework

Change-Id: I3c2c76a45ed75aaf67671b02649ba6abc24be083

stackalytics/processor/config.py

@@ -36,4 +36,8 @@ OPTS = [
                help='The address dashboard listens on'),
     cfg.IntOpt('listen-port', default=8080,
                help='The port dashboard listens on'),
+    cfg.StrOpt('corrections-uri',
+               default=('https://raw.github.com/stackforge/stackalytics/'
+                        'master/etc/corrections.json'),
+               help='The address of file with corrections data'),
 ]