Migrate client

• adding github eoxc/prism/ repository as client/ with its complete history (originally coming from github eoxc/mundi)
• built js file now named vsclient.js instead of prism.js
• two stage build for production using node for building library and lightweight nginx for serving static files
• one stage build for development - docker build -f client/Dockerfile.dev -t registry.gitlab.eox.at/esa/prism/vs/pvs_client:dev client/ utilizing node and webpack dev-server allowing hot-reload in running dev stack
• update bumpversion script to also bump client package.json and package-lock.json
• install corsheaders django plugin and configure it for DEV=true env - added to dev renderer&registrar services in compose files (we do not know which one will do the configuration)
• mount dev client instead of using docker config
• closes #80 (closed)