Add Sinopia indexer application and container

[mjgiarlo]

connects to #46 connects to #47 connects to LD4P/sinopia_indexing_pipeline#1

Includes:

• Add a sinopia_indexer folder with a simple JavaScript application, ported over from sinopia_client, that:
  • Connects to stomp to listen for messages from Trellis
  • Parses (Trellis) URIs out of stomp messages
  • Hits Trellis API to get JSON-LD representation of a changed Trellis resource
  • Indexes the JSON in ElasticSearch
• Containerize indexer application (using dockerize to wait on dependencies)
• Add indexer service to docker-compose configuration
• Prefer depends_on to no-longer-recommended links declarations in docker-compose config
• Add sinopia_client's package-lock.json
• Corrects license field and adds repository field to both package-lock.json files to get rid of warnings on npm install
• Ignore node_modules wherever it appears in the codebase

Needs:

• Test coverage
• README documentation
• One or two refactorings of the application (to be more class-oriented and less procedural)
• Add es6 linter/beautifier?
• More sophisticated indexing—I suspect we shouldn't be indexing the entire JSON-LD document for a Trellis resource
• Possibly: a change in how the indexer interacts w/ Trellis. Current assumption is that the activity stream messages will contain a Trellis resource URI that the indexer can GET without knowledge of the sinopia_server's internal workings

[jermnelson]

Hi @mjgiarlo , I like how you decomposed the script into separate javascript modules; very much the practice in React and Redux. I would suggest using Jest for your unit tests when you get to that point (if you haven't already).