increase API rate limits

[tmkis2]

using tools like dnscontrol that relies heavily on desec API usage the API rate limits are way too low.
Having 60 domains and checking for required updates will result in 60 requests in read api and probably 60 write api requests when an update is needed.

Perhaps a "pro plan" for users who have many domains they regulary check and update via API?

(Example: Assigned Domain Limit * 2 = allowed read/write requests per hour)