Better error handling when portions of falcor request fail

[LukeTillman]

Add better error handling and indications in the UI when parts of a Falcor JSON graph return error objects. This should include, for example, not leaving the "Loading" spinner showing indefinitely in video lists.

[jeffreyscarpenter]

A possible instance of this issue was discovered in implementing the KillrVideo Python services. In the SuggestedVideosService, when a list of video IDs is provided to the "get number of plays" operation, if some of the videos do not yet have any statistics in the database, that video was omitted from the results. The killrvideo-web application does not respond well when no stats are returned for one of the videos requested - it appears to "hang" with spinny ball and an error mentioning "views" not existing is found in the console. @mando222