Add bitcoin-wallet to the debian package

Summary: The tool is currently missing from the package.

Test Plan:
Build on Launchpad and search in the list of built packages for
bitcoin-wallet:
https://launchpad.net/~fabcien/+archive/ubuntu/bitcoin-abc/+build/20101041
Note: the bitcoind package contains both bitcoind and bitcoin-cli.

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7731