Consolidate CLI volume scanning code

[joachimmetz]

Consolidate CLI volume scanning code in examples, plaso and several other CLI tools into dfVFS

• [x] ~~Move code from recursive_hasher example into dfVFS helpers~~
  • ~~https://github.com/log2timeline/dfvfs/pull/340~~
  • ~~update wiki~~
• [x] ~~Update list_file_entries example to use dfVFS CLI helper~~
  • ~~https://github.com/log2timeline/dfvfs/pull/342~~
• [x] ~~https://github.com/log2timeline/dfvfs/pull/344~~
  • ~~add support for output writer and input reader~~
  • ~~add support for APFS~~
  • ~~add test coverage~~
  • ~~add support for Partition ranges~~
• [x] ~~add support for encrypted APFS~~
  • ~~https://github.com/log2timeline/dfvfs/pull/348~~
• [x] ~~https://github.com/log2timeline/dfvfs/pull/346~~
  • ~~add support for scan options/configuration~~
  • ~~add support for VSS current volume~~
• [ ] refactor to have generic volume system and volume snapshot mediator functions
• [ ] Improve test coverage

Originally from: https://github.com/log2timeline/plaso/issues/109

• [ ] Store scanning options in VolumeScanOptions objects ?
  • https://codereview.appspot.com/340700043/
  • make VolumeShadowSnapshotsOptions more generic?
  • move part of this functionality into dfvfs