Restructure cherrypy application more correctly

Specifically, switch from using global configuration and several apps,
to using application-specific configuration with a single app.  This
should hopefully make it easier to plug this into another
WSGI-compliant server someday, and also silences some startup warnings
about missing application configs.

nilmdb/server/server.py

@@ -391,25 +391,32 @@ class Server(object):
         # into it from separate threads.
         self.embedded = embedded
         self.db = nilmdb.utils.Serializer(db)
+
+        # Build up global server configuration
         cherrypy.config.update({
             'server.socket_host': host,
             'server.socket_port': port,
             'engine.autoreload_on': False,
             'server.max_request_body_size': 4*1024*1024,
-            'error_page.default': self.json_error_page,
             })
         if self.embedded:
             cherrypy.config.update({ 'environment': 'embedded' })
 
+        # Build up application specific configuration
+        app_config = {}
+        app_config.update({
+            'error_page.default': self.json_error_page,
+            })
+
         # Send a permissive Access-Control-Allow-Origin (CORS) header
         # with all responses so that browsers can send cross-domain
         # requests to this server.
-        cherrypy.config.update({ 'response.headers.Access-Control-Allow-Origin':
-                                 '*' })
+        app_config.update({ 'response.headers.Access-Control-Allow-Origin':
+                            '*' })
 
         # Send tracebacks in error responses.  They're hidden by the
         # error_page function for client errors (code 400-499).
-        cherrypy.config.update({ 'request.show_tracebacks' : True })
+        app_config.update({ 'request.show_tracebacks' : True })
         self.force_traceback = force_traceback
 
         # Patch CherryPy error handler to never pad out error messages.
@@ -417,11 +424,13 @@ class Server(object):
         # error messages.
         cherrypy._cperror._ie_friendly_error_sizes = {}
 
-        cherrypy.tree.apps = {}
-        cherrypy.tree.mount(Root(self.db, self.version), "/")
-        cherrypy.tree.mount(Stream(self.db), "/stream")
+        # Build up the application and mount it
+        root = Root(self.db, self.version)
+        root.stream = Stream(self.db)
         if stoppable:
-            cherrypy.tree.mount(Exiter(), "/exit")
+            root.exit = Exiter()
+        cherrypy.tree.apps = {}
+        cherrypy.tree.mount(root, "/", config = { "/" : app_config })
 
         # Shutdowns normally wait for clients to disconnect.  To speed
         # up tests, set fast_shutdown = True