Basic threading support

CMakeLists.txt

io.github.NhekoReborn.Nheko.yaml

resources/icons/ui/bookmark-disabled.svg

resources/icons/ui/bookmark.svg

resources/icons/ui/dismiss_thread.svg

resources/icons/ui/needle.svg

resources/icons/ui/new-thread.svg

resources/icons/ui/thread.svg

resources/qml/MessageInput.qml

resources/qml/MessageView.qml

resources/qml/ReplyPopup.qml

resources/qml/TimelineRow.qml

resources/res.qrc

src/Cache.cpp

src/Cache_p.h

src/timeline/EventStore.cpp

src/timeline/InputBar.cpp

src/timeline/InputBar.h

src/timeline/TimelineModel.cpp

src/timeline/TimelineModel.h