Throw exception if click("#selector") is done on wrong selector.

I started to try the example and used a wrong selector in the click-Method.
```java
public class LoginPage extends FluentPage {
..
        click("#wrong-selector");
..
```
No button got clicked and it was difficult to find the reason.
If click is done on wrong selector nothing has been done. Now if you do
a click with wrong selector a NoSuchElementException is thrown.