descpage: Implement loading, parsing and updating

To be able to change file description page, we need to load current
text, do manipulations and to update with new text

Issue #1 (#1)

euroexchange/config.py

@@ -43,3 +43,4 @@ class Config():
     zip_file = jogobot.config["euroexchange"]["data_zip_filename"]
     csv_file = jogobot.config["euroexchange"]["data_csv_filename"]
     upload_comment = jogobot.config["euroexchange"]["upload_comment"]
+    gnuplot_script_comment = jogobot.config["euroexchange"]["gnuplot_script_comment"]