Created ReplayAsset interface and AssetRepository class which can contain such ReplayAssets. ReplayAssets allow users to add custom Files (so far only images, might be extended by .obj files) to the Replay which will later be used for CustomImageObjects.

Created GuiReplayManager to allow users to manage their assets.
Created BoundingUtils class to provide a simple method to fit an image into given bounds. This implementation fixes https://trello.com/c/WTnicWkJ/

src/main/java/eu/crushedpixel/replaymod/assets/ReplayImageAsset.java

@@ -0,0 +1,85 @@
+package eu.crushedpixel.replaymod.assets;
+
+import eu.crushedpixel.replaymod.registry.ResourceHelper;
+import eu.crushedpixel.replaymod.utils.BoundingUtils;
+import net.minecraft.client.Minecraft;
+import net.minecraft.client.gui.Gui;
+import net.minecraft.client.renderer.texture.DynamicTexture;
+import net.minecraft.util.ResourceLocation;
+import org.lwjgl.util.Dimension;
+
+import javax.imageio.ImageIO;
+import java.awt.image.BufferedImage;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.util.UUID;
+
+public class ReplayImageAsset implements ReplayAsset<BufferedImage> {
+
+    private final Minecraft mc = Minecraft.getMinecraft();
+
+    private BufferedImage object;
+
+    private String name;
+
+    public ReplayImageAsset(String name) {
+        this.name = name;
+    }
+
+    @Override
+    public void setAssetName(String name) {
+        this.name = name;
+    }
+
+    @Override
+    public String getDisplayString() {
+        return name;
+    }
+
+    @Override
+    public String getSavedFileExtension() {
+        return "png";
+    }
+
+    @Override
+    public void loadFromStream(InputStream inputStream) throws IOException {
+        this.object = ImageIO.read(inputStream);
+        ResourceHelper.freeResource(previewResource);
+    }
+
+    @Override
+    public void writeToStream(OutputStream outputStream) throws IOException {
+        ImageIO.write(object, "png", outputStream);
+    }
+
+    @Override
+    public BufferedImage getObject() {
+        return object;
+    }
+
+    private ResourceLocation previewResource = new ResourceLocation("/asset/"+ UUID.randomUUID().toString());
+    private DynamicTexture dynamicTexture;
+
+    @Override
+    public void drawToScreen(int x, int y, int maxWidth, int maxHeight) {
+        if(object == null) return;
+        if(!ResourceHelper.isRegistered(previewResource) || dynamicTexture == null) {
+            dynamicTexture = new DynamicTexture(object);
+            mc.getTextureManager().loadTexture(previewResource, dynamicTexture);
+            ResourceHelper.registerResource(previewResource);
+        }
+
+        mc.renderEngine.bindTexture(previewResource);
+
+        Dimension dimension = BoundingUtils.fitIntoBounds(new Dimension(object.getWidth(), object.getHeight()), new Dimension(maxWidth, maxHeight));
+
+        Gui.drawScaledCustomSizeModalRect(x, y, 0, 0, object.getWidth(), object.getHeight(), dimension.getWidth(), dimension.getHeight(), object.getWidth(), object.getHeight());
+    }
+
+    @Override
+    protected void finalize() throws Throwable {
+        ResourceHelper.freeResource(previewResource);
+        super.finalize();
+    }
+}