Dockerfile accepts git checkouts

Dockerfile

@@ -1,26 +1,24 @@
 # Stage 0, "build-stage", based on Node.js, to build and compile the frontend
 FROM node:10 as build-stage
 
-# set working dir
 WORKDIR /app
-
-# Set the package files first, so they can be cached
-COPY client/package*.json ./
+ARG REPOSITORY_URL=https://github.com/OpenSlides/openslides-client.git
+ARG GIT_CHECKOUT=master
+RUN git clone --no-checkout -- $REPOSITORY_URL .
+RUN git checkout $GIT_CHECKOUT
 
 # install npm dependencies, should be cached
+WORKDIR /app/client
 RUN npm install
 
-# Copy the angular client code
-COPY client/ ./
-
 # compile the angular project
 RUN npm run build
 
 # Stage 1, based on Nginx, to have only the compiled app, ready for production with Nginx
 FROM nginx:latest
 
 # Copy the compildes app to nginx
-COPY --from=build-stage /app/dist /usr/share/nginx/html
+COPY --from=build-stage /app/client/dist /usr/share/nginx/html
 
 # Copy the nginx.conf
-COPY nginx/nginx.conf /etc/nginx/nginx.conf
+COPY --from=build-stage /app/nginx/nginx.conf /etc/nginx/nginx.conf