Custom data views: Offer a dedicated way to save changes

[jameskoster]

Saving changes to a custom data view is currently batched together with changes to the site itself:

When initially creating the view this level of gravity is perhaps warranted. However, when you're temporarily adjusting an existing view it feels a bit heavy-handed. Generally these are 'softer' edits that you wouldn't expect to persist. For example when you view Trash in wp-admin the date filter is inactive, regardless of whether you previously filtered by date or not.

We might consider the following adjustments to the save flow for custom views;

1. Including a "Save" action in the view menu.
2. Indicating the view has been customised somehow.
3. Not alerting the user of unsaved changes when navigating away.

A rough mockup:

cc @WordPress/gutenberg-design

[jasmussen]

Good issue.

The custom views, at the moment, feel a bit like an open question to me; I think they hold great potential long term, especially with just the right UI (for pinning, unpinning, deleting, moving, user role management, plugin management, all sorts of other things to explore), so I wonder if this nascent time is the right time to explore optimizations for the current set of features. I'd almost be tempted to keep the custom view aspect plugin only for a while still, until we have a solid path forward for these concepts.