Add file uploading

resources/qml/ActiveCallBar.qml

resources/qml/MessageInput.qml

resources/qml/NhekoBusyIndicator.qml

resources/qml/TimelineView.qml

resources/qml/VideoCall.qml

resources/res.qrc

src/ChatPage.cpp

src/ChatPage.h

src/TextInputWidget.cpp

src/TextInputWidget.h

src/Utils.cpp

src/Utils.h

src/dialogs/PreviewUploadOverlay.cpp

src/dialogs/PreviewUploadOverlay.h

src/timeline/InputBar.cpp

src/timeline/InputBar.h

src/timeline/TimelineModel.h