optimize `ScheduleHandler`s

[Tch1b0]

Previously it was planned to support multiple different guilds accessing their dsbmobile account, which is not the case anymore The scope of an instance of the bot is to just use one single dsbmobile account & class name.

For every single guild that binds the bot, a new ScheduleHandler is generated, which fires its own fetches and events. This is not optimal, as the bot is requesting the same resource over and over again.