Several packaging fixes.

it didn't fail before when building tahoe-lafs directly, I don't know
why (something else pulls in setuptools but it's unclear what).

it does fail without this when running the system tests at integration time...

other approach fails because we cannot upgrade pytest to fix attrs
incompatiblity because pytest has dropped python 2.7 support in 5.x series

Newer typing in nixpkgs requires newer Hypothesis than it has.

come back and explain this if it does :/

Expose ZKAPAuthorizer in python27Packages

Improve Tahoe-LAFS packaging

They fail a lot so leave them disabled.

The Nix packaging for PrivacyPass

OpenSSL 1.1.1c for Nix env

Fixes: #27 

openssl_1_1 in the pinned version of nixpkgs is 1.1.1c.

Create a `ci` profile and select it.

Fixes: #25 

This gives us deterministic, portable (across time) builds w/ nix.

Put ZKAPs into and take ZKAPs out of a database

Fixes: #18