Silences Listing Experience

[gotjosh]

What would you like to be added:

On the new alerting UI for silences, there's two things that I feel we could do to improve the experience of them:

1. When displaying the alerts, given “alertname” is selected as a key attributed it could have a two-level grouping where you could nest all the alerts with the same name under the same “level”.

2. The number of seconds is a bit hard to understand it could follow the style of >60s use minutes, >60m use hours, etc

Why is this needed:

It would aid with the UI experience when operating on silences.