fix spelling errors

INSTALL

src/call.cpp

src/callmodel.cpp

src/certificate.cpp

src/contactmodel.cpp

src/contactrequest.cpp

src/conversationmodel.cpp

src/credentialmodel.cpp

src/database.h

src/interfaces/itemmodelstateserializeri.h

src/itembase.cpp

src/personmodel.h

src/phonedirectorymodel.cpp

src/private/vcardutils.cpp

src/useractionmodel.cpp

src/video/sourcemodel.cpp

test/conversationmodeltester.cpp

test/datatransfertester.h