Update various debian packaging files

Summary:
This replaces "Bitcoin Core" with "Bitcoin ABC"
in various files in contrib/debian.

Comes from looking at some of the packaging scripts
that users have been contributing in /r/bitcoinabc .

Test Plan: check that the debian packages build

Reviewers: #bitcoin_abc, deadalnix, sickpig

Reviewed By: #bitcoin_abc, deadalnix, sickpig

Subscribers: ethernomad

Differential Revision: https://reviews.bitcoinabc.org/D347