Addresses 2 issues:
1) If a single plugin class implemented both the Worker and Notifier interfaces, multiple instances of the class were created, meaning no shared state within the plugin. Now only 1 instance is created.
2) Plugins implementing only Notifier weren't properly loaded.
The first time you click "Start monitor" (assuming you haven't read-all), we read the last 2 log files to find the journal entries for the last system jumped into (if we can find the FSDJump entry) in order to re-populate the information in all interested plugins. Its much faster than reading all to restore current system context.
- For Botanist plugin, this will display what plants/planets you've already sampled and avoids placeholder planet entries with incorrect bio counts.
- For Explorer, it re-lists interesting items, in case you weren't done exploring the system.
See https://github.com/Xjph/ObservatoryCore/issues/5
Upon arrival of new records to the backing ObservableCollection, scroll the DataGrid to the last item. However, when the DataGrid is initialized, there's not yet a data context set, so when that happens, then we can listen to the CollectionChanged event to trigger scrolling (only really needed for additions).
In passing, also set the DataGrid to ReadOnly.
In the other two files, minor simplifications/cleanup.
