Add migration to enable trackChanges for all users

migrations/6_add_track_changes_feature.coffee

+Settings = require "settings-sharelatex"
+fs = require("fs")
+mongojs = require("mongojs")
+ObjectId = mongojs.ObjectId
+db = mongojs(Settings.mongo.url, ['users'])
+_ = require("underscore")
+BSON = db.bson.BSON
+
+
+handleExit = () ->
+	console.log('Got signal.  Shutting down.')
+
+
+process.on 'SIGINT', handleExit
+process.on 'SIGHUP', handleExit
+
+
+exports.migrate = (client, done=()->) ->
+	patch = {
+		$set: {
+			'features.trackChanges': true
+		}
+	}
+	console.log ">> enabling trackChanges feature: ", patch
+	db.users.update {}, patch, {multi: true}, (err) ->
+		console.log "finished enabling trackChanges feature"
+		return done(err)
+
+
+exports.rollback = (client, done) ->
+	done()