widgets: feature implementation tracking: desirable

I'm adding this list here for now, but I plan to create an issue for each of those in the future.
Feel free to comment about new ones, so I can add them here.

- [x] Constrain widget moving and scaling (e.g.: outside the window)
- [x] Make widget development simple
- [ ] Create insightful widget template
- [x] Allow scaling from several mouse-positions (other than bottom-right corner)
- [x] Allow auto-scaling widgets to max-width/max-height
- [x] Allow auto-scaling widgets to full-screen
- [ ] Allow auto-snapping widgets to screen corners
- [ ] Allow auto-snapping widgets to other widgets
- [ ] Show help-lines when positioning widgets
- [ ] Allow changing layers ordering
- [ ] Allow naming layers
- [ ] Allow naming widgets
- [x] Focus widget when hovering it in the summary list
- [x] Maybe use navigation-drawer instead of edit window
- [ ] Add Photoshop/Gimp-like layer editing
- [ ] Use tree-view for layer ordering
- [x] Warn user before deleting layer/widget
- [ ] Allow undo/redo of user actions
- [x] Show overlay over widgets with info about them while in edit-mode
- [ ] Allow changing grid size
- [ ] Make layers somewhat transparent on edit-mode
- [ ] Allow enabling/disabling widgets border
- [ ] Allow freezing widget rendering while in edit-mode
- [x] Tint or focus widgets while in edit-mode to make positioning easier
- [x] Show resizing icon
- [x] Allow changing the canvas/background color/image
- [ ] Allow receiving events from internal-widgets

This issue is an umbrella checklist for widget features rather than a single task, and it names no files, tests, or entry points. Start by selecting one unchecked widget item and locating the corresponding widget-editing code; define completion and a focused test before implementing it.

Written by the indexing model from the issue text.