restructure into "server" and "ui" subdirs

Besides being more clear about what belongs to which, this helps with
docker caching. The server and ui parts are only rebuilt when their
respective subdirectories change.

Extend this a bit further by making the webpack build not depend on
the target architecture. And adding cache dirs so parts of the server
and ui build process can be reused when layer-wide caching fails.

docker/dev-common.bash

@@ -0,0 +1,68 @@
+#!/bin/bash
+# Build the "dev" target. See Dockerfile.
+
+set -o errexit
+set -o pipefail
+set -o xtrace
+
+export DEBIAN_FRONTEND=noninteractive
+
+packages=()
+
+apt-get update
+
+# Add yarn repository.
+apt-get --assume-yes --no-install-recommends install curl gnupg ca-certificates
+curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add -
+echo "deb https://dl.yarnpkg.com/debian/ stable main" \
+    >> /etc/apt/sources.list.d/yarn.list
+
+# Install all packages necessary for building (and some for testing/debugging).
+packages+=(
+    build-essential
+    pkgconf
+    locales
+    nodejs
+    sudo
+    sqlite3
+    tzdata
+    vim-nox
+    yarn
+)
+apt-get update
+apt-get install --assume-yes --no-install-recommends "${packages[@]}"
+apt-get clean
+rm -rf /var/lib/apt/lists/*
+
+# Create the user. On the dev environment, allow sudo.
+groupadd \
+    --gid="${BUILD_GID}" \
+    moonfire-nvr
+useradd \
+    --no-log-init \
+    --home-dir=/var/lib/moonfire-nvr \
+    --uid="${BUILD_UID}" \
+    --gid=moonfire-nvr \
+    --shell=/bin/bash \
+    --create-home \
+    moonfire-nvr
+echo 'moonfire-nvr ALL=(ALL) NOPASSWD: ALL' >>/etc/sudoers
+
+# Install Rust. Note curl was already installed for yarn above.
+su moonfire-nvr -lc "curl --proto =https --tlsv1.2 -sSf https://sh.rustup.rs |
+                     sh -s - -y"
+
+# Put configuration for the Rust build into a new ".buildrc" which is used
+# both (1) interactively from ~/.bashrc when logging into the dev container
+# and (2) from a build-server RUN command. In particular, the latter can't
+# use ~/.bashrc because that script immediately exits when run from a
+# non-interactive shell.
+echo 'source $HOME/.buildrc' >> /var/lib/moonfire-nvr/.bashrc
+cat >> /var/lib/moonfire-nvr/.buildrc <<EOF
+source \$HOME/.cargo/env
+
+# Set the target directory to be outside the src bind mount.
+# https://doc.rust-lang.org/cargo/reference/config.html#buildtarget-dir
+export CARGO_BUILD_TARGET_DIR=/var/lib/moonfire-nvr/target
+EOF
+chown moonfire-nvr:moonfire-nvr /var/lib/moonfire-nvr/.buildrc