Dgraph: Add a schema quick link query to Ratel Dashboard

[vespertilian]

As a new user I find the generic query below super helpful to understand what the database schema looks like, especially after I have run a few different example mutations. I feel it would be worthwhile to have this query as a quick link in your Ratel Dashboard for other newbies. I found the query on your docs site but it's a bit hidden away.

schema {
  type
  index
  reverse
  tokenizer
}

If you want to go even further, you could have a tab that just runs this query and returns clickable predicate. These clickable predicates could autogenerate a sample query, so you can explore the data mostly just by clicking around.

Just a though.
Dgraph seems really great so far.

[pawanrawal]

We could also think about building the functionality to mark certain queries as the favorite so that they can be accessed quickly.

[gpahal]

A schema tab has been added to the dashboard that you might useful.