TodoMVC Example

This issue tracks Blitz feature that need to be implemented and bugs that need to be fixed for Blitz to support Dioxus's TodoMVC example:

### Bugs
- [x] Panic when creating multiple tasks
- [x] Tasks disappear when editing completes
- [x] Inset shadows render incorrectly
- [ ] The "toggle all" button doesn't display

### Features
- [x] Background images (SVG)
- [ ] Inline elements: border/padding
- [x] Inline elements: hover/click events
- [x] Text input (clip text)
- [x] CSS transitions
- [x] Open external links in web browser on click
- [x] Dioxus double-click events
- [x] Focus
- [x] Dioxus focus events (specifically focusout)
- [x] Body should take focus when clicking somewhere with no other focus target