Add new subsccription param. 'failOnEmpty'

[daviddawson]

Add a new sub param 'failOnEmpty'

When this is set to 'true' and subscribed stream does not exist (ie, no events in that stream), then Photon should respond with a single event of type 'NoSuchStream' and then immediately issue the complete signal, closing the connection.

[daviddawson]

This can be worked around in my case by using stream-type:'cold' and checking to see if numitems.length>0