DetectorScene improvements + fixed integration regions

• Refactored DetectorScene extensively: removed unused members broke up over-nested functions, moved functionality into different classes.
• Move all methods that generate PeakCollection-related graphics from DetectorScene to new class PeakCollectionGraphics
• Move all methods that generate DataSet-related graphics from DetectorScene to new class DetectorSceneGraphics
• Removed MaskHandler class since lifetime of mask graphic objects was unpredictable and causing segfaults.
• Fixed issues with masks, graphical masks were not reflected correctly in core algorithms.
• Added separate parameters for fixed integration regions to avoid confusion
• Removed RegionType::FixedSphere, I can't imagine it ever being useful.
• No longer store pointers to subclassed QGraphicsItems when they are in the DetectorScene, since their lifetimes are too unpredictable.
• Handle failure to generate graphical items for DetectorScene with std::optional.
• Greatly reduced number of DetectorScene parameters, added many to new DetectorSceneParams header.
• New base class for BoxMaskItem and EllipseMaskItem, MaskItem, to facilitate adding/removing them from scene.
• Removed all code for generating graphics from Subframe classes, move to PeakCollectionGraphics/DataSetGraphics.
• Added name of DataSet associated with a PeakCollection to relevant SubframeHome table.
• Fixed bug in MaskImporter (arguments of AABB, lower and upper bounds were reversed).

Resolves #582 (closed), #581 (closed), #228 (closed), #578 (closed) and #583 (closed)