hoodie.store.hasLocalChanges()

```js
hoodie.store.hasLocalChanges()
// < false

hoodie.store.add({name: 'BMO'})
.then(function(object) {
  hoodie.store.hasLocalChanges()
  // < true
})
.then(hoodie.store.push)
.then(function () {
  hoodie.store.hasLocalChanges()
  // < false
})
```

Please add tests, too