eventhub: application properties is not sent

[davidt99]

On version 1.3.2, if I set an application properties key, the properties are not sent:

event_data = EventData(json.dumps({'test': 1}))
event_data.application_properties['foo'] = 'bar'
sender.send(event_data)

The thing is, if I initialize the application properties as a new dictionary, it works:

event_data = EventData(json.dumps({'test': 1}))
event_data.application_properties = {'foo: 'bar'}
sender.send(event_data)

The problem lies here:
https://github.com/Azure/azure-event-hubs-python/blob/master/azure/eventhub/common.py#L92 where this dict is not propagated to the Message object created in line #105
That repo is no longer maintained but I'm not interested in using a SDK which is still in beta status.

[kaerm]

@davidt99 thanks again :) - routing it the right way. //cc: @yunhaoling