Adds lock file and requirements files as required for packaging

[kushaldas]

Adds requirements-* files required for packaging.

[redshiftzero]

There's a permissions change on qubes/securedrop.Proxy - is that intentional?

[kushaldas]

There's a permissions change on qubes/securedrop.Proxy - is that intentional?

Yes, those files are supposed to be executable.

[redshiftzero]

ok, thanks for clarifying (for changes like that it's probably worth noting in a commit message). otherwise looks good!

For posterity, one cannot reproducibly build the wheel packages in order to verify the *.whl hashes due to this upstream issue: freedomofpress/securedrop-debian-packaging-guide#3 (comment)