Idea: Automatically discover allowed_updates

[TiiFuchs]

We are able to identify the used update types the bot handles and could filter the update types the bot receives in the beginning by passing it as allowed_updates
to setWebhook or getUpdates.

This would reduce network traffic and resources, since we don't need to load the framework and parse the whole incoming json data before going over all handlers and find that there are no responsible handlers.

[TiiFuchs]

There should be an option to deactivate this behaviour though.