TAK Server reporting multiple user subscriptions within TAK Server

[CoryFoy]

As seen in the below screenshot, when TAK Tracker is connecting to a TAK Server it is registering itself multiple times. In addition, the call sign is not being populated in the server subscriptions

[CoryFoy]

This is now fixed in the latest TestFlight build (1.16). It was the culmination of two issues:

1. The TAK Server requires an additional contact and uid node in detail of the CoT to properly identify the user. This commit reworks the XML processing to pull everything into structs and then adds the new nodes in place.
2. We had a race condition where a connection would be attempting to spin up, but because we weren't connected yet when we'd go to send a CoT message we'd attempt to reconnect, spinning up multiple connections. This is fixed in this commit to ensure we're reusing a single connection and properly tracking the state of its lifecycle.

For issue 1 - though things seem to be working right now, this comment from PyTAK seems to imply we may be missing another use case here. Will have to watch for that in testing.