Time for action – writing a luminance threshold filter

Let's append a new component to our UI and implement the new image filter.

1. Add a new Threshold SeekBar and Button in res/activity_renderscript.xml:

   <?xml version="1.0" encoding="utf-8"?>
   <LinearLayout
     xmlns:a="http://schemas.android.com/apk/res/android"
     a:layout_width="fill_parent" a:layout_height="fill_parent"
     a:layout_weight="1" a:orientation="vertical" >
     <LinearLayout 
       a:orientation="horizontal"
       a:layout_width="fill_parent" a:layout_height="wrap_content" >
       ...
       <SeekBar a:id="@+id/thresholdBar" a:max="100"
         a:layout_gravity="center_vertical"
         a:layout_width="128dp" a:layout_height="wrap_content" />
       <Button a:id="@+id/thresholdButton" a:text="Threshold"
         a:layout_width="wrap_content" a:layout_height="wrap_content"/>
     </LinearLayout>
     <LinearLayout 
       a:baselineAligned="true" a:orientation="horizontal"
       a:layout_width="fill_parent" a:layout_height...