Logging: Add customizable logging backends and fmtlib based macros

* Change the logging backend to support multiple sinks through the
Backend Interface
* Add a new set of logging macros to use fmtlib instead.
* Qt: Compile as GUI application on windows to make the console hidden by
default. Add filter configuration and a button to open log location.
* SDL: Migrate to the new logging macros

src/core/settings.cpp

@@ -4,14 +4,13 @@
 
 #include "audio_core/dsp_interface.h"
 #include "core/core.h"
+#include "core/frontend/emu_window.h"
 #include "core/gdbstub/gdbstub.h"
 #include "core/hle/service/hid/hid.h"
 #include "core/hle/service/ir/ir.h"
 #include "core/settings.h"
 #include "video_core/video_core.h"
 
-#include "core/frontend/emu_window.h"
-
 namespace Settings {
 
 Values values = {};

src/core/settings.h

@@ -129,8 +129,6 @@ struct Values {
     float bg_green;
     float bg_blue;
 
-    std::string log_filter;
-
     // Audio
     std::string sink_id;
     bool enable_audio_stretching;
@@ -143,6 +141,7 @@ struct Values {
     // Debugging
     bool use_gdbstub;
     u16 gdbstub_port;
+    std::string log_filter;
 
     // Movie
     std::string movie_play;