Initial implementation of custom price triggers

- likely to have some bugs, but this is good enough for a preview release.

token_bot/persistant_database/alert_schema.py

@@ -99,7 +99,8 @@ class Alert:
 
     def to_human_string(self):
         if self.alert_type == AlertType.SPECIFIC_PRICE:
-            raise NotImplementedError
+            price_gold = self.price
+            return f"Custom Price: {format(price_gold, ',')}g"
         else:
             alert_type_str = " ".join(self.alert_type.name.split("_"))
             return f"{alert_type_str.title()}"