Fixing CenterLayout

See merge request redox-os/orbtk!100

The CenterLayout needed to behave more like the FixedSizeLayout because the centered objects should logically have a larger space to be centered in. The bounds of the internal child object need to use the full layout size to set the internal origin.

Added a depth parameter to the expand function to support pretty-printing the view hierarchy in debug mode.

Example:
```
| MainView (id = 1, children_len = 1)
| | Row (id = 2, children_len = 1)
| | | Column (id = 3, children_len = 5)
| | | | Container (id = 4, children_len = 1)
| | | | | TextBlock (id = 5, children_len = 0)
| | | | Container (id = 6, children_len = 1)
| | | | | Button (id = 7, children_len = 1)
```

Pretty print view hierarchy

See merge request redox-os/orbtk!99

Added a depth parameter to the expand function to support pretty-printing the view hierarchy in debug mode.

Example:
```
| MainView (id = 1, children_len = 1)
| | Row (id = 2, children_len = 1)
| | | Column (id = 3, children_len = 5)
| | | | Container (id = 4, children_len = 1)
| | | | | TextBlock (id = 5, children_len = 0)
| | | | Container (id = 6, children_len = 1)
| | | | | Button (id = 7, children_len = 1)
```

fix typo

See merge request redox-os/orbtk!97