Implement album tracks pattern matching in Artist

This is risen by the ongoing Artist view of the QT interface, where albums are shown together with their tracks. The QT team need an efficient way to filter albums based on their track content.

This should be do-able just by adding a filter parameter to the already existing Artist function:

    // New filter parameter introduced
    enum class SearchMode : uint8_t {
        /// Apply pattern matching on album title, artist and tracks.
        All,
        /// Apply pattern matching on album title and artist only.
        TitleAndArtist,
    };
    virtual Query<IAlbum> searchAlbums( const std::string& pattern,
                                        SearchMode mode = SearchMode::TitleAndArtist,
                                        const QueryParameters* params = nullptr ) const = 0;