chatview: add toast on file saved

src/app/commoncomponents/SBSContextMenu.qml

src/app/constant/JamiStrings.qml

src/app/mainview/components/FilePreview.qml

src/app/mainview/components/MediaPreview.qml

src/app/mainview/components/MessageListView.qml

src/app/messagesadapter.cpp

src/app/messagesadapter.h

src/libclient/api/datatransfermodel.h

src/libclient/datatransfermodel.cpp