make Settings.parallelSqlQueryLimit a config setting

app/coffee/DbQueue.coffee

@@ -1,9 +1,10 @@
 async = require "async"
+Settings = require "settings-sharelatex"
 
 queue = async.queue((task, cb)->
 		console.log("running task")
 		task(cb)
-	, 1)
+	, Settings.parallelSqlQueryLimit)
 
 queue.drain = ()->
     console.log('HI all items have been processed')

config/settings.defaults.coffee

@@ -36,6 +36,7 @@ module.exports =
 	smokeTest: process.env["SMOKE_TEST"] or false
 	project_cache_length_ms: 1000 * 60 * 60 * 24
 	parallelFileDownloads:1
+	parallelSqlQueryLimit:1
 	filestoreDomainOveride: process.env["FILESTORE_DOMAIN_OVERRIDE"]
 	texliveImageNameOveride: process.env["TEX_LIVE_IMAGE_NAME_OVERRIDE"]