Add "ratio" attribute to component styles

As discussed at https://github.com/Jasonette/documentation/issues/62

Ratio refers to aspect ratio (width/height)

Example:

```
{
"type": "image",
"url": "file://image.jpg",
"style": {
"width": "100px",
"ratio": "1.0"
}
}
```

Start by reading the referenced documentation issue 62, then locate how component styles are handled in the Android project. Confirm how the width and ratio example should affect component layout, and verify that the ratio attribute works for the described image style without breaking existing styles.

Written by the indexing model from the issue text.