Convert ClassLoader.getSystemResource* calls to class.getResource* variant for OSGi, etc. safety

src/main/java/org/qora/controller/Controller.java

@@ -80,7 +80,7 @@ public class Controller extends Thread {
 
 	private Controller() {
 		Properties properties = new Properties();
-		try (InputStream in = ClassLoader.getSystemResourceAsStream("build.properties")) {
+		try (InputStream in = this.getClass().getResourceAsStream("/build.properties")) {
 			properties.load(in);
 		} catch (IOException e) {
 			throw new RuntimeException("Can't read build.properties resource", e);

src/main/java/org/qora/gui/Gui.java

@@ -42,9 +42,9 @@ public class Gui {
 	}
 
 	protected static BufferedImage loadImage(String resourceName) {
-		try (InputStream in = ClassLoader.getSystemResourceAsStream("images/" + resourceName)) {
+		try (InputStream in = Gui.class.getResourceAsStream("/images/" + resourceName)) {
 			return ImageIO.read(in);
-		} catch (IOException e) {
+		} catch (IllegalArgumentException | IOException e) {
 			LOGGER.warn(String.format("Couldn't locate image resource \"images/%s\"", resourceName));
 			return null;
 		}