Add UNKNOWN and SPACE key

graphics/src/main/java/de/staropensource/sosengine/graphics/types/input/Key.java

@@ -27,6 +27,13 @@ package de.staropensource.sosengine.graphics.types.input;
  */
 @SuppressWarnings({ "unused" })
 public enum Key {
+    /**
+     * An unknown key.
+     *
+     * @since v1-alpha2
+     */
+    UNKNOWN,
+
     /**
      * The left mouse button.
      *
@@ -732,6 +739,12 @@ public enum Key {
      * @since v1-alpha2
      */
     SLASH,
+    /**
+     * The {@code ENTER} key.
+     *
+     * @since v1-alpha2
+     */
+    SPACE,
     /**
      * The {@code TAB} key.
      *