Improvements to the Study Status card

In the cases

* waiting
* error

the study status card could be improved. When waiting there is an empty containier, which makes the ui jump up and down and when an error an ugly text string is shown. This can be improved - the code is here

```
builder: (context, snapshot) {
if (snapshot.connectionState == ConnectionState.waiting) {
return Container();
} else if (snapshot.hasError) {
return Padding(
padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 22),
child: Text('Error: ${snapshot.error}'),
); // Show an error message if t
```