Add image "adder", queue, save, and export button to vSLAM Sandbox GUI

[vadixidav]

Currently, vslam-sandbox operates by taking all images to run at the command line. We should augment this by allowing images to be added through either drag-and-drop or a file chooser onto the GUI. This would replace passing this at the command line. Adding images will add them to a queue. There will also be a button to queue up a save of the reconstruction state to the GUI. Additionally, there will be a button to export to PLY. The settings for these can still be retrieved from the command line within the scope of this issue.