Add ancestor images info in view

[demoulinv]

Description

This PR adds information in a view about ancestor images of this view. This is useful for example when an HDR image is created from a set of LDR images. In a view associated to the new HDR image, we store all information about all LDR images. With those changes, sfmData version is upgraded to 1.2.6.

Corresponding Meshroom PR: https://github.com/alicevision/Meshroom/pull/2242

Features list

• [X] View update (including deep copy)
• [X] Json importer / exporter update
• [X] Alembic importer / exporter update
• [X] Unitary test update

Implementation remarks