The code on FxMixerView.cpp and FxMixer.cpp were using the types TrackContainer::TrackList and QVector<Track *> unconsistently. TrackContainer::TrackList is just a typedef for QVector<Track *> so it makes sense that we use it, specially in terms of readability.

Places where QVector<Track *> were used are now replaced with TrackContainer::TrackList.

Also, we were not including "TrackContainer.h" directly (the typedef was likely being included indirectly through one of the other include files), so we also include this header on both source codes.