Add a general ExceptionInterface

[Toflar]

Should make things easier if multiple calls are made in the same code:

try {
    $repo = new Repository('ssh://.....git');
    $branch = $repo->getBranch('main');
} catch (use Ausi\RemoteGit\ExceptionInterface) {
    // Do not care which one it is, just something with the connection or branch does not fit.
}