Added Elasticsearch status to 'GET /_ping'
Added Elasticsearch status to 'GET /_ping'

We use Chewy for Elasticsearch, checking health of cluster tells us
if Elasticsearch is okay or not.

Fixes #424

mkcode/classroom,ConnorCartwright/classroom,BelieveC/classroom,mkcode/classroom,BelieveC/classroom,mkcode/classroom,BelieveC/classroom,BelieveC/classroom,ConnorCartwright/classroom,ConnorCartwright/classroom