Rename contrib/debian/* files to use blackcoin prefix

Signed-off-by: Xerxes Rånby <xerxes@gudinna.com>
contrib/debian/* rebrand to blackcoin

Signed-off-by: Xerxes Rånby <xerxes@gudinna.com>
don't mention nonexistent blkindex.dat
Merge branch 'debian' of https://github.com/xranby/blackcoin