Ladybird: Use only the Qt event loop to speed everything up :^)

This patch removes the dual-event-loop setup, leaving only the Qt event
loop. We teach LibWeb how to drive Qt by installing an EventLoopPlugin.

This removes the 50ms latency on all UI interactions (and network
requests, etc.)

Ladybird/CMakeLists.txt

@@ -49,6 +49,7 @@ set(SOURCES
     ConsoleClient.cpp
     ConsoleGlobalObject.cpp
     CookieJar.cpp
+    EventLoopPluginQt.cpp
     RequestManagerQt.cpp
     main.cpp
     WebView.cpp
@@ -56,6 +57,7 @@ set(SOURCES
     Settings.cpp
     SettingsDialog.cpp
     Tab.cpp
+    TimerQt.cpp
 )
 
 qt_add_executable(ladybird ${SOURCES}