Disable interactive Debian frontend to squelch warnings

This silences warnings such as the following:

    debconf: unable to initialize frontend: Dialog
    debconf: (TERM is not set, so the dialog frontend is not usable.)
    debconf: falling back to frontend: Readline
    debconf: unable to initialize frontend: Readline
    debconf: (This frontend requires a controlling tty.)
    debconf: falling back to frontend: Teletype
    dpkg-preconfigure: unable to re-open stdin:
Set the locale
Additional comments
Ignore `keys/*`
Remove apt-get mirror method support
Install LLVM alongside the haskell toolchain