introduce DC_EVENT_NEW_BLOB_FILE event and test for it

deltachat-ffi/deltachat.h

@@ -3924,6 +3924,16 @@ int64_t          dc_lot_get_timestamp     (const dc_lot_t* lot);
  */
 #define DC_EVENT_IMAP_MESSAGE_MOVED   105
 
+/**
+ * Emitted when a new blob file was successfully written 
+ *
+ * @param data1 0
+ * @param data2 (const char*) path name 
+ *     Must not be free()'d or modified and is valid only until the callback returns.
+ * @return 0
+ */
+#define DC_EVENT_NEW_BLOB_FILE 150
+
 /**
  * The library-user should write a warning string to the log.
  * Passed to the callback given to dc_context_new().