api: datstore status: introduce proper structs and restore compatibility

api: datstore status: introduce proper structs and restore compatibility

by moving the properties of the storage status out again to the top
level object

also introduce proper structs for the types used, to get type-safety
and better documentation for the api calls

this changes the backup counts from an array of [groups,snapshots] to
an object/struct with { groups, snapshots } and include 'other' types
(though we do not have any at this moment)

this way it is better documented

this also adapts the ui code to cope with the api changes

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>