Some QML properties access exposed Python objects that may or may not
be null upon their access. When these objects are accessed while null,
QML issues "TypeError" warnings. These warnings have no functional
impact as QML correctly handles trying to access null objects, but can
spam the logs.
This commit aims at fixing all these warnings by checking that the
Python objects are not null before being accessed.
Handle nodes move and auto-layout on Python side by using GraphLayout and MoveNodeCommand.
* Node QML component relies on underlying core.Node object's position
* MoveNodeCommand is called after a Node has been dragged
* partial/full auto-layout for specific graph operations (Duplication, Augmentation...) are now part of those operations
* serialized position in node data allows to properly restore nodes coordinates on undo/redo
* remove all layout/node moving code from QML
* move LiveSfmManager.stepCreated to Reconstruction.sfmAugmented
* add utility methods in Reconstruction to get all images/views used in the graph
* ui: perform local auto-layout on sfm augmentation on created nodes
