Add Data Feeds Status to UI

## Current Behavior:

There is no datafeed status in the UI anywhere that I can find. To me, this is related to #265, which asks that a Test connection feature be added for each connection that has to have credentials.

### Proposed Behavior:

Add some status content somewhere, like in the About dialog, or a new page that lists all the possible datafeeds and provides info like:

Feed 1 (disabled)
Feed 2 (enabled): Status: OK <-- or whatever happened (e.g., can't connect, login failed, download interrupted), Last sink: Date/Time
etc.