Reconsider `SubscriptionStatus` and it's handlers

[FranjoMindek]

Now that we have access to more payment processors we should reconsider SubScriptionStatus implementation.
One good thing would be to better generalize our status names.

Currently we have:

export enum SubscriptionStatus {
  PastDue = 'past_due',
  CancelAtPeriodEnd = 'cancel_at_period_end',
  Active = 'active',
  Deleted = 'deleted',
}

One problem we have is that we have a state called CancelAtPeriodEnd but then that leads to Deleted rather than Canceled state.
This is also problematic if we want to support both Canceled and Deleted states in the future, where Deleted could be e.g. forced deletion of the subscription status like in Stripe sandbox mode.

[FranjoMindek]

We should also reconsider how we handle SubscriptionStatus transitions.
We have a start of an idea for the current implementation here: #569 (comment)