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.

test/bacnet/basic/object/device/CMakeLists.txt

@@ -80,6 +80,7 @@ add_executable(${PROJECT_NAME}
     ${SRC_DIR}/bacnet/basic/object/schedule.c
     ${SRC_DIR}/bacnet/basic/object/structured_view.c
     ${SRC_DIR}/bacnet/basic/object/time_value.c
+    ${SRC_DIR}/bacnet/basic/object/timer.c
     ${SRC_DIR}/bacnet/basic/object/trendlog.c
     ${SRC_DIR}/bacnet/basic/sys/bigend.c
     ${SRC_DIR}/bacnet/basic/sys/days.c
@@ -100,6 +101,7 @@ add_executable(${PROJECT_NAME}
     ${SRC_DIR}/bacnet/proplist.c
     ${SRC_DIR}/bacnet/property.c
     ${SRC_DIR}/bacnet/reject.c
+    ${SRC_DIR}/bacnet/timer_value.c
     ${SRC_DIR}/bacnet/timestamp.c
     ${SRC_DIR}/bacnet/wp.c
     ${SRC_DIR}/bacnet/weeklyschedule.c