Add soft update support

[AVAtarMod]

I was read about TW Snapshots problem: At the system update if in the system exists apps with dependencies, which is newer, then snapshot can proposal, then these apps can be a break after an update or may happen something worse

My proposal:

• add options "--soft-install" which not downgrade packages at the update and perform actions only on packages which not need downgrade' or
• create list apps, which need save from breaking and their dependencies downgrade not allowed