Initial docker support

Dockerfile

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+#####################################################
+### Build UI bundles
+FROM node:12.14-alpine AS jsbuilder
+WORKDIR /src
+COPY ui/package.json ui/package-lock.json ./
+RUN npm ci
+COPY ui/ .
+RUN npm run build
+
+
+#####################################################
+### Build executable
+FROM golang:1.13-alpine AS gobuilder
+
+# Download build tools
+RUN mkdir -p /src/ui/build
+RUN apk add -U --no-cache build-base git
+RUN go get -u github.com/go-bindata/go-bindata/...
+
+# Download project dependencies
+WORKDIR /src
+COPY go.mod go.sum ./
+RUN go mod download
+
+# Copy source and UI bundle, build executable
+COPY . .
+COPY --from=jsbuilder /src/build/* /src/ui/build/
+COPY --from=jsbuilder /src/build/static/css/* /src/ui/build/static/css/
+COPY --from=jsbuilder /src/build/static/js/* /src/ui/build/static/js/
+RUN rm -rf /src/build/css /src/build/js
+RUN make buildall
+
+# Download and unpack static ffmpeg
+ARG FFMPEG_VERSION=4.1.4
+ARG FFMPEG_URL=https://www.johnvansickle.com/ffmpeg/old-releases/ffmpeg-${FFMPEG_VERSION}-amd64-static.tar.xz
+ADD ${FFMPEG_URL} /tmp/ffmpeg.tar.xz
+RUN cd /tmp && tar xJf ffmpeg.tar.xz
+
+
+#####################################################
+### Build Final Image
+FROM alpine
+COPY --from=gobuilder /src/sonic-server /app/
+COPY --from=gobuilder /tmp/ffmpeg*/ffmpeg /usr/bin/
+
+VOLUME ["/data", "/music"]
+ENV SONIC_DBPATH /data/cloudsonic.db
+ENV SONIC_MUSICFOLDER /music
+ENV SONIC_LOGLEVEL info
+EXPOSE 4533
+
+WORKDIR /app
+CMD "/app/sonic-server"