Show NPS labels instead of placeholder scores in reporting/ClientGrid/Slack notifications

Instead of showing -100, show "Detractor", instead of showing 0, show "Passive", instead of 100, show "Promoter" as actual scores could be anywhere between -100 and 100 (or on an entirely different scale) and this helps avoid unnecessary alarm - especially when leveraging Slack where not all users will have CS licenses to check the details.