* add the notion of a current SfM node in the Reconstruction
* retrieve views and poses from this node when selected or when its status changes
* use this information to display a status on Images in ImageGallery
* keep an internal reference to the "main" CameraInit node an update it according to graph modification
* expose viewpoints model as a property
* TODO: handle multiple CameraInit nodes
* extract UIGraph from Reconstruction: base class that wraps a core.Graph, without knowledge of photogrammetry pipeline
* ChunksMonitor: watch NodeChunks status files for external changes to keep UI updated even when the graph is being computed externally
* Reconstruction inherits UIGraph with photogrammetry specific features
* add methods to add images to the reconstruction (DropEvent or urls)
* explicitly call CameraInit's buildIntrinsics method
* update CameraInit with resulting views and intrinsics
First functional UI that allows to visualize, modify and execute a graph locally.
* use QtQuick Controls 2 + Shapes (Qt >=5.10)
* main menu to save/load a graph
