Daikin176: Add support for Unit Id. (#1544)

* Add `IRDaikin176:setId()` & `IRDaikin176:getId()` for dealing with Unit Identifiers.
* Add "Id:" to `.toString()` output.
* Add unit test coverage for that, and update existing tests.
* Misc code style cleanups.

Fixes #1543

Author: crankyoldgit