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.

src/bacnet/basic/object/bo.c

@@ -1032,7 +1032,7 @@ int Binary_Output_Read_Property(BACNET_READ_PROPERTY_DATA *rpdata)
     uint8_t *apdu = NULL;
     int apdu_size = 0;
 
-    if ((rpdata->application_data == NULL) ||
+    if ((rpdata == NULL) || (rpdata->application_data == NULL) ||
         (rpdata->application_data_len == 0)) {
         return 0;
     }