Combine BeforeInput and Composition event plugins

In order to improve support for Chinese and Japanese IME input in
Internet Explorer, use a fallback composition state to determine
inserted text. IE composition events are mostly okay, except for
certain punctuation characters that are ignored. Using the fallback, we
can detect these characters.

The fallback is also useful for emitting `beforeInput` events, so it
makes sense to simply combine these plugins.

This change also incorporates a recent change to the Google Input Tools
browser extension that exposes a `data` field via the `detail` object
on the custom composition events it emits.
Update BeforeInputEventPlugin.js
Merge pull request #2690 from salier/before-input

Combine BeforeInput and Composition event plugins