Rule proposal: no undefined styles

Similar to #2, it would be nice to have a rule that enforces the inverse: using styles that are not defined.

Bad:

``` jsx
function MyComponent({ styles }) {
return (

export default withStyles(() => ({
foo: {
backgroundColor: 'red',
},
}))(MyComponent);
```

Good:

``` jsx
function MyComponent({ styles }) {
return (

export default withStyles(() => ({
foo: {
backgroundColor: 'red',
},

bar: {
color: 'white',
},
}))(MyComponent);
```

Start by reviewing the related issue #2 and the repository's existing rule structure and tests. Define the rule's handling of style references such as styles.foo and styles.bar, then add coverage showing that every referenced style is defined before considering the work complete.

Written by the indexing model from the issue text.