Added basic timer object, internal state machine, and unit tests (#1123)

* Added basic timer object, internal state machine, and unit tests

* Added BACnetTimerStateChangeValue encode, decode, parse, print, and diff with unit tests

* Changed handler of add/remove list element to check if the property is a BACnetLIST

* Added BACnetLIST utility for handling WriteProperty to a list.

* Fixed outlier ReadProperty object handlers to return zero when the RP parameter is NULL.

apps/server-mini/Makefile

@@ -37,6 +37,7 @@ SRC = main.c \
 	$(BACNET_OBJECT_DIR)/netport.c  \
 	$(BACNET_OBJECT_DIR)/program.c  \
 	$(BACNET_OBJECT_DIR)/time_value.c \
+	$(BACNET_OBJECT_DIR)/timer.c \
 	$(BACNET_OBJECT_DIR)/trendlog.c \
 	$(BACNET_OBJECT_DIR)/schedule.c \
 	$(BACNET_OBJECT_DIR)/structured_view.c \