* Replace masonry with gridstack
* Initial work on dashboard widgets
* Implement function to save dashboard layout
* Define a default dashboard
* Clean up widgets
* Implement widget configuration views & forms
* Permit merging dict value with existing dict in user config
* Add widget deletion view
* Enable HTMX for widget configuration
* Implement view to add dashboard widgets
* ObjectCountsWidget: Identify models by app_label & name
* Add color customization to dashboard widgets
* Introduce Dashboard model to store user dashboard layout & config
* Clean up utility functions
* Remove hard-coded API URL
* Use fixed grid cell height
* Add modal close button
* Clean up dashboard views
* Rebuild JS
