Improve mobile design

We might consider removing line 796 of `glowingbear.js` as well:
```javascript
    if ($rootScope.isMobileUi()) {
        nonicklist = true;
        noembed = true;
        notimestamp = true;  // remove this line?
        $rootScope.wasMobileUi = true;
    }
```
It sets the *default behaviour* (doesn't override user preference) to hiding the timestamps

![screenshot](https://4z2.de/gb-mobiledesign.png)