[mobile] support dark theme - part 1

app/src/main/res/color/nav.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <selector xmlns:android="http://schemas.android.com/apk/res/android">
-    <item android:color="@color/accent" android:state_checked="true" />
+    <item android:color="?attr/colorControlNormal" android:state_checked="true" />
     <item android:color="@color/white" android:state_checked="false" />
 </selector>

app/src/mobile/res/layout/dialog_update.xml

@@ -19,7 +19,7 @@
             android:layout_height="wrap_content"
             android:letterSpacing="0.02"
             android:lineSpacingExtra="8dp"
-            android:textColor="@color/grey_900"
+            android:textColor="?android:attr/textColorPrimary"
             android:textSize="14sp"
             tools:text="1. 新增 ffmpeg 音頻軟解\n2. 詳情頁新增分詞快搜\n3. 修復搜尋閃退問題\n4. 設定支援渲染切換" />