Update exceptions

[Nyholm]

Before releasing 2.0 we need to update all the places we are using HTTPlug exceptions. Example the Jounal interface has a dependency on a HTTPlug exception and cannot be used with PSR-18.

[Nyholm]

Here is the only interface that we have an exception in: https://github.com/php-http/client-common/blob/master/src/Plugin/Journal.php#L32

If one do a search for use Http\Client\Exception then one will find all the places. I think we should update that to PSR-18 exception on all places.