Extract key action types to their respective classes.

model/KeyAction.ts

@@ -5,11 +5,11 @@ class KeyAction {
 
     static fromJsObject(jsObject: any): KeyAction {
         switch (jsObject.keyActionType) {
-            case 'none':
+            case KeystrokeAction.actionTypeString:
                 let keyActionNone = new KeyActionNone();
                 keyActionNone.fromJsObject(jsObject);
                 return keyActionNone;
-            case 'keyStroke':
+            case KeystrokeAction.actionTypeString:
                 let keystrokeAction = new KeystrokeAction();
                 keystrokeAction.fromJsObject(jsObject);
                 return keystrokeAction;

model/KeyActionNone.ts

@@ -2,6 +2,7 @@
 /// <reference path="Serializable.ts" />
 
 class KeyActionNone extends KeyAction implements Serializable {
+    static actionTypeString = 'none';
     static keyActionNoneId = 0;
     static keyActionNoneParam = 0;
 

model/KeystrokeAction.ts

@@ -3,6 +3,7 @@
 
 class KeystrokeAction extends KeyAction implements Serializable {
 
+    static actionTypeString = 'keyStroke';
     static firstValidScancode = 1;
     static lastValidScancode = 231;