Add ability to store deprecated/abandoned information

If a plugin changes their coordinates such as:

```
com.bertramlabs.plugins:asset-pipeline-grails:2.14.2
org.grails.plugins:asset-pipeline:3.2.1
```

It would be good to have the ability to specify something either in the metadata or on the site it's superseded by a different plugin.

Maybe also in the list view as well a badge or something.