allow backup of signle or multiple specific vm's. And improve internal workings

Additions:

• add: "allow_using_any_existing_snapshot" this makes it possible to have multiple backup intervals per vm
• add: remove backups
• add: transport compression support
• add: cli "restore-point info"
• add: lazy load vm config to avoid unnecessary proxmox api requests
• add documentation / checklist for manual vm config and vm disk restore
• add: backup vm's matching regex
• add: "get_snapshot_current" which returns the actual current snapshot
• add: "wait_for_snapshot_tries" config option

Fixes:

• fix: eqality implementation of VM objects

Changes:

• change: remove proxmox dummy snapshot from "get_snapshots" function
• change: Backup.remove_vm_snapshot() now awaits removal completion
• change: change utcnow() to now(), for now ;)

Removals:

• remove option and implementation of "--whole-object" due to bug in rbd export-diff (Bug #42248)