Update to Bevy 0.8

* UiCameraBundle has been removed. Ui camera is now on-by-default.
  - bevyengine/bevy#4745
* Rect is now UiRect
* Text::with_section() is now Text::from_section() and alignment is set with with_alignment
```rust
Text::from_section(
    "Score",
    TextStyle {
        font: font_spec.family.clone(),
        font_size: 15.0,
        color: Color::WHITE,
    }).with_alignment(
    TextAlignment {
        vertical: VerticalAlign::Center,
        horizontal: HorizontalAlign::Center,
    },
),
```
* QuerySet is now ParamSet
* OrthographicCameraBundle is now Camera2dBundle::default()