Work in progress.

Applied callSync's in DlgAutoDJ, DlgMissing; added callSyncs to
BaseExternalLibraryFeature. Added init() method to SetlogFeature, so
rewrited code in Library c-tor. Moved initialization of
m_pLibraryTableModel (in MixxxLibraryFeature::init) to c-tor
initialization list. Added methods SetlogFeature::init() and
SetlogFeature::constructChildModel().