Fixed warnings about unused parameters.
Moved constructor to implementation.

Avoids having copy of the vtable in _every_ file which includes the
header.
Fixed finding of Qt4 and Phonon.

Not sure if it was Arch-specific problem or screwed up generally.
Work-around -fvisibility=hidden compilation issues.

It seems that Arch's Qt4 now requires that.
Adapt also "official" Arch PKGBUILD to recent qt -> qt4 change.