Success/failure notifications on batch actions

[chillu]

Acceptance Criteria

• I can clearly see the outcome of a batch operation (delete, move, publish, unpublish)
• The success message details how many items were affected
• If any items failed (e.g. due to the user lacking permissions), the message shows warning/error styling and details which items failed
• The message can be dismissed by the user

Excludes

• Retry
• Links to the individual items
• Loading indicators, see https://github.com/silverstripe/silverstripe-admin/issues/176

Notes

• Notifications should be consistent between sections - @newleeland do we have design patterns for different notification levels yet?
• This came out of "batch publish/unpublish", see https://github.com/silverstripe/silverstripe-asset-admin/issues/525
• Initial designs from @newleeland at https://projects.invisionapp.com/share/3RD5LSAJE#/screens/249886649

[newleeland]

@chillu at the moment, notification patterns split between two types of actions, -Banner notifications for or actions (edit/move/delete) and -Popup notifications for completion actions (publish/unpublish)

Currently every action within files area results in a banner notification and all page actions lead to popup notifications However, it would be good to have all the (publish/unpublish) actions feedback with popup notifications as they disappear rather than stack like banner notifications.