[Android] Fix some redundancy in the category names for the settings …

…menu. In a menu named "Settings" (which is shown in the top left) we have the categories, "CPU Settings" and "Video Settings" - but the fact they are settings pages is already established at this point so it's redundant. Just made them "CPU" and "Video" instead.

Also changed the description for dual-core

They now look like this: http://i.imgur.com/qieaKmL.png

Source/Android/res/values-ja/strings.xml

@@ -62,7 +62,7 @@
     <string name="cpu_settings">CPU設定</string>
     <string name="emu_core_to_use">使用するエミュレーションコア</string>
     <string name="dual_core">デュアルコア</string>
-    <string name="on_off">有効/無効</string>
+    <string name="dual_core_descrip">有効にした場合、デュアルコアが使用されます。</string>
     <string name="video_settings">ビデオ設定</string>
     <string name="software_renderer">Software Renderer</string>
     <string name="opengl_es3">OpenGL ES 3</string>

Source/Android/res/values/strings.xml

@@ -59,11 +59,11 @@
     <string name="jitil_recompiler">JITIL Recompiler</string>
     <string name="jit_arm_recompiler">JIT ARM Recompiler</string>
     <string name="cpu_core">CPU Core</string>
-    <string name="cpu_settings">CPU Settings</string>
+    <string name="cpu_settings">CPU</string>
     <string name="emu_core_to_use">Emulation core to use</string>
     <string name="dual_core">Dual Core</string>
-    <string name="on_off">On/Off</string>
-    <string name="video_settings">Video Settings</string>
+    <string name="dual_core_descrip">Whether or not to use dual-core</string>
+    <string name="video_settings">Video</string>
     <string name="software_renderer">Software Renderer</string>
     <string name="opengl_es3">OpenGL ES 3</string>
     <string name="video_backend">Video Backend</string>

Source/Android/res/xml/cpu_prefs.xml

@@ -3,7 +3,7 @@
     <!-- CPU Settings -->             
     <CheckBoxPreference
            android:key="dualCorePref"
-           android:summary="@string/on_off"
+           android:summary="@string/dual_core_descrip"
            android:title="@string/dual_core" />
 
     <ListPreference