Extract Automation & System Domain Models

[baync180705]

Move the data structures from automation/automation.go, output/json.go and output/tarball.go into the internal/domain package.

Requirements:

• Create internal/domain/automation.go. Copy SystemDUnit, Cronjob, AutomationData structs here.
• Create internal/domain/metadata.go. Copy the SystemInfo struct (from output/json.go) and BackupData, EncryptedKey, Dotfile, BackupMetadata struct (from output/tarball.go)
• Update automation.go, tarball.go and json.go to import internal/domain and use these types.
• Code should work as expected without crashing.