Renamed docker/4_run/deploy to docker/4_run/staging

"Staging" covers the meaning of what is actually happening better than
"deploy". I want to keep "deploy" for actually deploying onto a production
server.

docker/4_run/Dockerfile

@@ -57,7 +57,7 @@ ENTRYPOINT /docker-entrypoint.sh
 
 # Add the most-changing files as last step for faster rebuilds.
 ADD config_local.py /data/git/blender-cloud/
-ADD deploy /data/git
+ADD staging /data/git
 RUN python3 -c "import re, secrets; \
 f = open('/data/git/blender-cloud/config_local.py', 'a'); \
 h = re.sub(r'[_.~-]', '', secrets.token_urlsafe())[:8]; \