Fix issue where uppercase style names weren't read in IE8

Converts all style strings to lowercase so that correct `colorData` hex value can be plugged in for named colors in IE8.

Previously the following would color nodes with a weird black color in IE8:

```
Node: {
            height: 60,
            width: 180,
            type: 'rectangle',
            color: 'LightCyan',
            overridable: true
        }
```

but this would work:
```
Node: {
            height: 60,
            width: 180,
            type: 'rectangle',
            color: 'lightcyan',
            overridable: true
        }
```