Fix Incorrect ChatScene Size on Startup (#79)

Additionally fixes error on message receival.
Fixes #68
Reviewed-on: https://git.kske.dev/zdm/envoy/pulls/79
Reviewed-by: kske <kai@kske.dev>
Reviewed-by: DieGurke <maxi@kske.dev>

client/src/main/resources/fxml/ChatScene.fxml

@@ -20,13 +20,17 @@
 <?import javafx.scene.layout.RowConstraints?>
 <?import javafx.scene.layout.VBox?>
 <?import javafx.scene.text.Font?>
+<?import javafx.stage.Screen?>
 
 <GridPane fx:id="scene" maxHeight="-Infinity"
 	maxWidth="-Infinity" minHeight="400.0" minWidth="500.0"
-	prefHeight="1152.0" prefWidth="2042.0"
+	prefHeight="${screen.visualBounds.height}" prefWidth="${screen.visualBounds.width}"
 	xmlns="http://javafx.com/javafx/11.0.1"
 	xmlns:fx="http://javafx.com/fxml/1"
 	fx:controller="envoy.client.ui.controller.ChatScene">
+	<fx:define>
+    	<Screen fx:factory="getPrimary" fx:id="screen" />
+	</fx:define>
 	<columnConstraints>
 		<ColumnConstraints hgrow="NEVER"
 			maxWidth="327.99997965494794" minWidth="-Infinity" prefWidth="317.0" />