wine build: use docker to (try to) have reproducible builds

contrib/build-wine/docker/Dockerfile

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+FROM ubuntu:18.04@sha256:5f4bdc3467537cbbe563e80db2c3ec95d548a9145d64453b06939c4592d67b6d
+
+ENV LC_ALL=C.UTF-8 LANG=C.UTF-8
+
+RUN dpkg --add-architecture i386 && \
+    apt-get update -qq && \
+    apt-get install -qq \
+        wget=1.19.4-1ubuntu2.1 \
+        gnupg2=2.2.4-1ubuntu1.1 \
+        dirmngr=2.2.4-1ubuntu1.1 \
+        software-properties-common=0.96.24.32.3 \
+        && \
+    wget -nc https://dl.winehq.org/wine-builds/Release.key && \
+    apt-key add Release.key && \
+    apt-add-repository https://dl.winehq.org/wine-builds/ubuntu/ && \
+    apt-get update -qq && \
+    apt-get install -qq \
+        winehq-stable=3.0.1~bionic \
+        git=1:2.17.1-1ubuntu0.1 \
+        p7zip-full=16.02+dfsg-6 \
+        make=4.1-9.1ubuntu1 \
+        mingw-w64=5.0.3-1 \
+        autotools-dev=20180224.1 \
+        autoconf=2.69-11 \
+        libtool=2.4.6-2 \
+        && \
+    rm -rf /var/lib/apt/lists/* && \
+    apt-get autoremove -y && \
+    apt-get clean

contrib/build-wine/docker/README.md

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+Deterministic Windows binaries with Docker
+==========================================
+
+This assumes an Ubuntu host, but it should not be too hard to adopt to another
+similar system.
+
+1. Install Docker
+
+    ```
+    $ curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
+    $ sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"
+    $ sudo apt-get update
+    $ sudo apt-get install -y docker-ce
+    ```
+
+2. Build image
+
+    ```
+    $ cd contrib/build-wine/docker
+    $ PROJECT_ROOT=$(pwd)/../../../
+    $ sudo docker build --no-cache -t electrum-wine-builder-img .
+    ```
+
+    Note: see [this](https://stackoverflow.com/a/40516974/7499128) if having dns problems
+
+3. Build Windows binaries
+
+    ```
+    $ TARGET=master
+    $ sudo docker run \
+        --name electrum-wine-builder-cont \
+        -v ${PROJECT_ROOT}:/opt/electrum \
+        --rm \
+        --workdir /opt/electrum/contrib/build-wine \
+        electrum-wine-builder-img \
+        ./build.sh $TARGET
+    ```
+4. The generated binaries are in `$PROJECT_ROOT/contrib/build-wine/dist`.
+
+
+
+Note: the `setup` binary (NSIS installer) is not deterministic yet.