feat: user can see 'modified' status in the dataset list

[chriswhong]

Depends on https://github.com/qri-io/qri/issues/841

User should be able to see at a glance if there are datasets in their dataset list that have uncommitted changes.

This can be an icon (the same as the modified icon for a dataset component) that appears in the list next to the dataset name.

[chriswhong]

This would still be desirable in the new collection view work