Add placeholder in Encoding menu

Since this has been causing a bit of confusion, the placeholder will let users know this is intentional. See #258

src/NotepadNext/dialogs/MainWindow.ui

@@ -233,11 +233,7 @@
     <property name="title">
      <string>Encoding</string>
     </property>
-   </widget>
-   <widget class="QMenu" name="menuRun">
-    <property name="title">
-     <string>Run</string>
-    </property>
+    <addaction name="actionThis_is_not_currently_implemented"/>
    </widget>
    <addaction name="menuFile"/>
    <addaction name="menuEdit"/>
@@ -247,7 +243,6 @@
    <addaction name="menuLanguage"/>
    <addaction name="menuSettings"/>
    <addaction name="menuMacro"/>
-   <addaction name="menuRun"/>
    <addaction name="menuHelp"/>
   </widget>
   <widget class="QToolBar" name="mainToolBar">
@@ -992,6 +987,14 @@
     <string>Edit Macros...</string>
    </property>
   </action>
+  <action name="actionThis_is_not_currently_implemented">
+   <property name="enabled">
+    <bool>false</bool>
+   </property>
+   <property name="text">
+    <string>This is not currently implemented</string>
+   </property>
+  </action>
  </widget>
  <layoutdefault spacing="6" margin="11"/>
  <customwidgets>