integrated key server look-up into decrypt Activity, allowing to touch an unkown signature to import the key

Update issue 39
added:
<string name="unknownSignatureKeyTouchToLookUp">Unknown signature, touch to look up key.</string>

res/layout/decrypt.xml

@@ -144,7 +144,8 @@
         android:id="@+id/signature"
         android:orientation="horizontal"
         android:layout_height="wrap_content"
-        android:layout_width="fill_parent">
+        android:layout_width="fill_parent"
+        android:clickable="true">
 
         <RelativeLayout
             android:layout_height="wrap_content"