Misc refinements

* Refine Kotlin codes;
* Support RTL;
* Use VectorDrawable for notification;
* Remove redundant resources;
* Better IDE integration.

mobile/src/main/java/com/github/shadowsocks/utils/Utils.kt

@@ -9,6 +9,7 @@ import android.support.v4.app.Fragment
 import android.support.v4.app.FragmentManager
 import android.support.v7.util.SortedList
 import android.util.DisplayMetrics
+import android.util.TypedValue
 import android.view.Gravity
 import android.view.View
 import android.view.Window
@@ -77,6 +78,8 @@ fun Toast.position(view: View, window: Window, offsetX: Int = 0, offsetY: Int =
     return this
 }
 
+fun Float.dp(): Float = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, this, app.resources.displayMetrics)
+
 /**
  * Based on: https://stackoverflow.com/a/15656428/2245107
  */