Added IsWriting event on common, server and partially on client side

additionally fixed NullPointerException in ContactSearchScene and typo
in Javadoc

PS: this is the 1000th commit in Envoy! 🥳 🎉

common/src/main/java/envoy/event/IsWriting.java

@@ -0,0 +1,53 @@
+package envoy.event;
+
+/**
+ * This event should be sent when a user wrote anything in a chat.
+ * <p>
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>IsWriting.java</strong><br>
+ * Created: <strong>24.07.2020</strong><br>
+ *
+ * @author Leon Hofmeister
+ * @since Envoy Client v0.2-beta
+ */
+public class IsWriting extends Event<Long> {
+
+	private final long destinationID;
+
+	private final String displayName;
+
+	private static final long serialVersionUID = 1L;
+
+	/**
+	 * The number of milliseconds that this event will be active.<br>
+	 * Currently set to 3.5 seconds.
+	 */
+	public static final int millisecondsActive = 3500;
+
+	/**
+	 * Creates a new {@code IsWriting} with originator and recipient.
+	 *
+	 * @param sourceID      the id of the originator
+	 * @param displayName   the name of the originator
+	 * @param destinationID the id of the contact the user wrote to
+	 * @since Envoy Client v0.2-beta
+	 */
+	public IsWriting(Long sourceID, long destinationID, String displayName) {
+		super(sourceID);
+		this.destinationID	= destinationID;
+		this.displayName	= displayName;
+	}
+
+	/**
+	 * @return the id of the contact in whose chat the user wrote something
+	 * @since Envoy Client v0.2-beta
+	 */
+	public long getDestinationID() { return destinationID; }
+
+	/**
+	 * @return the name of the originator to display
+	 * @since Envoy Common v0.2-beta
+	 */
+	public String getDisplayName() { return displayName; }
+
+}