more refinement of dockerfile & added stack needs

etc/docker/ubuntu-with-gnupg/Dockerfile

@@ -1,36 +1,44 @@
 FROM fpco/ubuntu-with-libgmp:14.04
 
-# INSTALL PACKAGES
+# PACKAGES
 ENV DEBIAN_FRONTEND noninteractive
 RUN apt-get update
-RUN apt-get -y install curl expect
+RUN apt-get -y install curl            ;# needed to install Nix
+RUN apt-get -y install expect          ;# needed to automate GPG key trust
+RUN apt-get -y install build-essential ;# needed by Stack at runtime
+RUN apt-get -y install libgmp-dev      ;# needed by Stack at runtime
+RUN apt-get -y install xz-utils        ;# needed by Stack at runtime
 
-# CREATE USER
+# USER
 ENV USER user
 ENV HOME /home/$USER
-RUN groupadd -r nixbld
-RUN useradd -m $USER -G nixbld
+RUN useradd -m $USER
+
+# GPG CONFIG & KEYS
 ADD .gnupg/ $HOME/.gnupg/
-RUN chown -R user:user $HOME
+RUN chown -R $USER:$USER $HOME
 RUN chmod -R go-rwsx $HOME
+
+# NIX DIR & GROUP
 RUN mkdir /nix
-RUN chown $USER:nixbld /nix
-WORKDIR $HOME
-USER $USER
+RUN chown -R $USER:$USER /nix
+RUN groupadd -r nixbld
 
 # INSTALL NIX
+CMD /bin/bash -l
+WORKDIR $HOME
+USER $USER
 RUN curl -s https://nixos.org/nix/install | sh
 RUN echo "\nsource /nix/var/nix/profiles/default/etc/profile.d/nix.sh" \
   | tee -a $HOME/.bash_profile
 
-# INSTALL GNUPGS & SETUP KEYS
+# GNUPG PROFILES
 RUN bash -lc "nix-env -p /nix/var/nix/profiles/gpg14 -iA nixpkgs.nix nixpkgs.gnupg1orig"
 RUN bash -lc "nix-env -p /nix/var/nix/profiles/gpg20 -iA nixpkgs.nix nixpkgs.gnupg20"
 RUN bash -lc "nix-env -p /nix/var/nix/profiles/gpg21 -iA nixpkgs.nix nixpkgs.gnupg"
 RUN bash -lc "nix-env -S /nix/var/nix/profiles/gpg14" ;# SET CURRENT PROFILE TO GPG 1.4
+
+# IMPORT & TRUST KEYS
 RUN bash -lc "gpg --import $HOME/.gnupg/public.asc $HOME/.gnupg/subkey.asc"
 RUN bash -lc "expect $HOME/.gnupg/trust"
 RUN rm $HOME/.gnupg/*.asc $HOME/.gnupg/trust
-
-# LOGIN SHELL
-CMD /bin/bash -l