Co-authored-by: Tom Prince <tom.prince@private.storage>

They're all redundant on Python 3

This means you can make estimates about storage-time remaining based on the
results of the calculator endpoint and they'll at least match your local
configuration.

also, move the function to the config module.

Take care not to spend them, though.

Now PaymentController has a set of these as an attribute.  It could possibly
consider making some decisions based on this value now.

The redeemer will submit this many tokens with its redemption request now.  It
needs to agree with whatever the issuer wants to do, of course.

The entire ZKAPAuthorizer client resource hierarchy is now protected by this
token, ensuring any callers at least have local filesystem access to the
Tahoe-LAFS node.

Runtime performance at 512000 is somewhat intolerable.  Further work is needed to support that scale.

Thanks, Hypothesis.