added warning level highlighting to dashboard
added warning level highlighting to dashboard

- 10% < |delta| < 30% : show yellow warning block
- |delta| > 30% : show red error block

Change-Id: I72e7a3074f520329f176bd3b20ad65537b07243f

couchbaselabs/litmus,couchbaselabs/litmus,couchbaselabs/litmus