Stub alert levels, see item:292
Imlement alertsFactory.success
Implement other alert levels
Depreceate add alert in tests
Replace alert calls with levels, deprecate add

**API change**: instead of

```js
alertsFactory.addAlert({type: 'success', message: 'message'});
```

… use:

```js
alertsFactory.success('message');
```

Closes item:292.
Merge pull request #137 from tlvince/refactor/aliased-alert-types

Replace alert calls with levels, deprecate add