Add ZigBeeUtcTime class and client/server

[cdjackson]

This is something I wrote a while back but didn't create a PR so I need to try and remember how it all works :)

This creates a ZigBeeUtcTime class for managing time on a remote device. It then supports a ZigBeeTimeExtension which in turn can provide a local ZclTimeClient or ZclTimeServer to manage the time on the remote device.

The ZclTimeServer is relatively simple in that it just responds to requests from the device.

The ZclTimeClient is in itself also simple in that it provides methods to set the time on the remote.

The ZigBeeTimeExtension tries to automate the time management by working out drift rates, and setting the clock proactively if the time has drifted outside spec and the device didn't update the time through a request to the ZclTimeServer.

There is also a ZigBeeConsoleTimeCommand console command to get or set the time, and display the various information.

This is potentially a breaking change if people are using time at the moment since this changes some interfaces from Calendar to ZigBeeUtcTime.

I welcome comments on this and will wait a week or two before merging.

Signed-off-by: Chris Jackson chris@cd-jackson.com

[dschall]

Hey chris, apologies, I still didn't have time to test. Thanks for coding this up, I hope to be able to run some testing soon...

[cdjackson]

@dschall I've updated this to use the ZclCommandListener - this should avoid multiple responses. I also updated some initialisation code to register the clusters and merged master into this so it's up to date.