Nouveau - Messages bulk actions need attention - mark read/unread functionality

[hnla]

Transposed from:
​https://github.com/buddypress/next-template-packs/issues/192

While the messages bulk actions mainly work ok and the hiding & showing of select option re-factored for visual display elements, there are a number of issues needing attention.

1/ mark unread/read - in Ajax terms sends a response ok yet does nothing apparent, no classes or obvious action performed, notifications not adjusted either.

2/ General UX not great - needs something ( i.e spinner gif) to show action occurring also screen success message located below messages preview pane and out of sight, needs moving and styling as other screen messages.

[imath]

1/ That's probably because the unread class wasn't styled. I've added it on this patch ​7731.2.patch

2/ We can add loading/feedback messages as suggested in the attached patch.

[imath]

In 12071:

BP Nouveau-Messages UI: ask the user to wait until bulk action is done

Fixes #7626