Dispose default preferences renderer when model is cleared

- Find matches in editable settings editor
- Focus matches first in editable and then default settings

The user is encouraged to check the exclude settings when there are no search
results. Previously this would just open up the settings without any indication
which settings are relevant. This change will update the search filter to show
`files.exclude` and `search.exclude`.

- Do not navigate by Enter from search box

- Down arrow to navigate from search to list