Code navigation

It would be nice to have source code navigation similar to:

1. https://sourcegraph.com/
2. Stash code navigator https://marketplace.atlassian.com/plugins/com.mohamicorp.stash.plugin.codenav/server/overview
3. http://www.codota.com/ (Sid has a contact)
4. maybe using ctags https://news.ycombinator.com/item?id=11421026

Not sure if this should utilize Elastic Search to power this.

/cc @JobV @dzaporozhets @stanhu

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