Update various debian packaging files
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
Differential Revision: https://reviews.bitcoinabc.org/D347