Added complete exception handling

Hi rithms,

I implemented full exception handling in your Library. In order to do so I had to change the way the API request is made in general, since I needed the http response codes which apache commons includes only partly.
Therefore I implemented a static class called Request that calls the Riot API.

All calls to the API now throw an exception including the reason for the error.
I haven't tested everything but I shouldn't have introduced any issues.

While implementing I fixed a few bugs here & there.

Let me know what you think.

Regards

FriesischScott