Pass msg_level and remove duplicated checks

This makes the Study Description page render again.
Hmm -- there is no reason that `level` or `message` need to be passed to the call to `render` ([see these lines in sitebase](https://github.com/biocore/qiita/blob/master/qiita_pet/templates/sitebase.html#L23-L36)).  A better fix here would be to redefine `display_template` to have default arguments for those parameters:
```python
def display_template(self, study, msg="", msg_level="", tab_to_display=""):
```