Feature/raspberry pi blinkt color objects (#503)

* fixed BACnetXYcolor and BACnetColorCommand encode and decoding and improved unit test coverage. Refactored BACnetXYcolor to/from ascii into lighting module.

* added to the color, color temperature, and lighting output objects a fade/ramp/step engine.  Added color and color command coercion into the channel object and enabled color temperature object coercion.  Added CreateObject and DeleteObject service handling to the color, color temperature, lighting output, and channel objects.

* added blinkt demo app for Raspberry Pi [WIP]

* updated gitignore to simplify handling of apps folder contents

* fixed piface demo build

* added RaspiOS to pipeline for piface and blinkt! demo builds

* added device object timer function for child object types into example Device object.  Refactored device object to increment database revision for create or delete object services.   Refactored example app/server to use mstimer library and device child object timers.

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Co-authored-by: Steve Karg <skarg@users.sourceforge.net>

apps/blinkt/README.md

@@ -0,0 +1,26 @@
+# Raspberry Pi connected to a Blinkt! RGB card demo
+
+This demo includes a BACnet server with Color objects and service handlers
+for the eight RGB (red-green-blue) LEDs attached to the Blinkt! card.
+
+## Installation
+
+The demo uses pigpiod (Pi GPIO Daemon) and developer library. To install 
+and run the daemon at powerup (and immediately):
+
+    $ sudo apt install libpigpio-dev libpigpiod-if-dev pigpiod
+    $ sudo systemctl enable pigpiod
+    $ sudo systemctl start pigpiod
+
+## Building
+    
+Build from the root folder:
+
+    $ make blinkt
+
+## Running
+
+Run from the bin/ folder:
+
+    $ ./bin/bacblinkt 9009
+