please export StyleSheetTestUtils

Hi!
First of all thanks for making this interface!

Is it possible to export the following test-utility function from aphrodite:
StyleSheetTestUtils

This would remove the need to add the complete aphrodite dependency to a project while only actually using `react-with-styles-interface-aphrodite`, just for testing purposes.

I'm currently only using this interface for the react-dates dateRangePicker component but the tests are currently throwing this error:
```typescript
styleTag = document.querySelector("style[data-aphrodite]")
^
TypeError: Cannot read property 'querySelector' of null
```

This issue can be solved by adding the following for each test:
```typescript
beforeEach(() => {
StyleSheetTestUtils.suppressStyleInjection();
});
afterEach(() => {
StyleSheetTestUtils.clearBufferAndResumeStyleInjection();
});
```

Since the `StyleSheetTestUtils` are not exported by `react-with-styles-interface-aphrodite` I'll need to install the complete aphrodite package just for testing, which feels like an overkill.

I'll prepare an PR for this.

Start at the react-with-styles-interface-aphrodite package entry point and inspect how StyleSheetTestUtils is currently imported or exposed. Verify the export by using the suppressStyleInjection and clearBufferAndResumeStyleInjection calls in the react-dates dateRangePicker tests, and confirm the null style query error is resolved.

Written by the indexing model from the issue text.