Rule to prohibit default exports

TSLint [has a similar rule](https://palantir.github.io/tslint/rules/no-default-export/), where it prohibits default exports. Basically this (second case generating a warning):

```js
// good-1.js
export function foo() {}

// good-2.js
function foo() {}
export {foo}

// bad-1.js
export default function foo() {}

// bad-2.js
function foo() {}
export {foo as default}
```