Conditional formatting of rows in Message Table while Dashboarding

## What?
Request to add conditional formatting of messages/logs in message table (in dasbhoard) to visually seperate messages for eg: CRITICAL/INFO/ERROR etc messages

## Why?

While analyzing real time log feeds it is important to have some way to visually distinguish messages that are coming in.
something like this.

something like this

Because we want live dashboarding this is critical thing to be implemented.
## Your Environment

* Graylog Version: 3.3
* Elasticsearch Version:6.x
* MongoDB Version:4.2
* Operating System:Centos