Add API for writable object property lists (#1206)

Added a new API for writable property lists across all the basic example object types, preparing for the introduction of a Writable_Property_List property in every object in a future BACnet standard revision.

The lists can be used by backup and restore feature to automatically choose the object property values in the backup that can be restored via internal WriteProperty directly from BACnet CreateObject services with  List of Initial Values. 

Updated existing device object examples to include these writable property lists.

src/bacnet/basic/object/timer.h

@@ -43,6 +43,10 @@ void Timer_Property_Lists(
     const int32_t **pOptional,
     const int32_t **pProprietary);
 BACNET_STACK_EXPORT
+void Timer_Writable_Property_List(
+    uint32_t object_instance, const int32_t **properties);
+
+BACNET_STACK_EXPORT
 bool Timer_Valid_Instance(uint32_t object_instance);
 BACNET_STACK_EXPORT
 unsigned Timer_Count(void);