Implement detailPredmetuPage.

Kedze tu nas zaujima iba KeyError z find_row, presunul by som zvysok z `try` sekcie do `else` sekcie (vid https://docs.python.org/3/tutorial/errors.html):
```
try:
    index = find_row(...)
except KeyError:
    index = None
    bla bla zatvor ho
else:
    bla bla select() a enterButton.click()
```