overlay: OBS control window via WebSocket API (#773)

## Link to GitHub Issue or related Pull Request, if one exists
n/a

## Description of change
Adds an overlay window widget for controlling OBS over WebSocket.

Add new lines to the FPS widget that shows recording / streaming timers.

Show notifications for major state changes (stream started/stopped,
recording started/paused/resumed/stopped)

## Testing

src/spice2x/overlay/overlay.cpp

@@ -50,6 +50,7 @@
 #include "windows/sdvx_sub.h"
 #include "windows/keypad.h"
 #include "windows/log.h"
+#include "windows/obs.h"
 #include "windows/patch_manager.h"
 #include "windows/exitprompt.cpp"
 
@@ -416,6 +417,12 @@ void overlay::SpiceOverlay::init() {
     }
     this->window_add(new overlay::windows::PatchManager(this));
 
+    // OBS control spawns a background WebSocket worker; skip it in the standalone
+    // configurator, where there is no running game to stream/record
+    if (!cfg::CONFIGURATOR_STANDALONE) {
+        this->window_add(window_obs = new overlay::windows::OBSControl(this));
+    }
+
     {
         window_keypad1 = new overlay::windows::Keypad(this, 0);
         this->window_add(window_keypad1);