Add extension support

Let's you do
```
chrome::extension { 'Reddit Enhancement Suite':
  id => 'kbmfpngjjgdllneeigpgjifpgocmfgmb',
}

chrome::canary::extension { 'Reddit Enhancement Suite':
  id => 'kbmfpngjjgdllneeigpgjifpgocmfgmb',
}

chrome::chromium::extension { 'Reddit Enhancement Suite':
  id => 'kbmfpngjjgdllneeigpgjifpgocmfgmb',
}
```

Since beta, dev and stable Chrome share the same profile there isn't a point in having `chrome::dev::extension`, etc.