Move the 'supports_file_requests' attribute into the actual modes rather than the Web class

cli/onionshare_cli/web/send_base_mode.py

@@ -52,6 +52,10 @@ class SendBaseModeWeb:
         # This tracks the history id
         self.cur_history_id = 0
 
+        # Whether or not we can send REQUEST_INDIVIDUAL_FILE_STARTED
+        # and maybe other events when requests come in to this mode
+        self.supports_file_requests = True
+
         self.define_routes()
         self.init()