Rework rendering pipeline to make better use of multithreading

Move OpenGL frame to ARGB conversion to processing threads
Move video exporting to processing threads
Skip creation of BufferedImage and instead use ByteBuffer with ARGB content directly

src/main/java/eu/crushedpixel/replaymod/video/rendering/FrameCapturer.java

@@ -0,0 +1,11 @@
+package eu.crushedpixel.replaymod.video.rendering;
+
+import java.io.Closeable;
+
+public interface FrameCapturer<R extends Frame> extends Closeable {
+
+    boolean isDone();
+
+    R process();
+
+}