ratman/dashboard: Add per-address bandwidth metrics

Issue Fix

Fixes #56 (closed)

Description

Adds basic metrics to the dashboard, by polling and parsing the Prometheus endpoint from the frontend.

Alternative(s) considered

The original implementation of this attempted to do the aggregation on the server side, which turned out to be... difficult. Doing it this way has the slight drawback that it only shows changes since the dashboard was opened, and all metrics will show as 0Kb/s for the first 5s as it waits for a second scrape to come around.

It also currently has a very simplistic model for doing so (it only checks the current and last sample), but that can be improved later.

Type

Choose one: Feature

Screenshots (if applicable)