<IconButton> should support 'size'

#### Issue:
- Using an ``, for example in an ``, it would be good to be able to add the `size` attribute in the same way we can when using an `` object.

#### Example:
```javascript
{/* React.JS based, these two lines have the same output */}

{/* These two lines have the desired output of the above */}

```

#### Expected result:
- Support small sized icons

Start by locating the IconButton and Icon components, then compare how the size attribute is handled for each within the ActionBarGroup example. Done means IconButton accepts a size value and produces the expected small icon output described in the issue.

Written by the indexing model from the issue text.