Plugin watchers don't work if another plugin is added later on

[dopenguin]

Describe the bug

In reverseGeocoder and pins the configuration parameters coordinateSources are being used to add watchers to react to changes in another plugins store. However, if the watched plugin is added with addPlugin after the plugin that is watching, the watcher can not be established.

Expected behavior

It should be possible to add plugins in any order and have watchers connect / disconnect on the fly.

Steps to reproduce

1. npm run snowbox
2. Setting a pin does not trigger a reverse geocode