Implement split-tile boundary visualizations

[kgabor]

Add support for Stephan's split tile approach.

• [x] Refactor the data model to support more than one kind of loaders
• [x] Add a data reader for the outer-inner split model
• [x] Add a grid model that can identify the outer and inner overlapping boundaries of the split-tiles
• [x] Add plotting support for a grid of sub-tiles in the projection plots
• [x] Add panel annotation for split tiles in the plots

[kgabor]

• [x] Add inner boundary plots
• [ ] Test with interestpoints to plot