ConfigurableExtension(PreferenceScreen) support (#163)

* initial PreferenceScreen support, works with 'NeoXXX Scans' (pt-br)

* convert EditTextPreference to json successfully

* commit what I've got

* bring back the old SharedPreferences for CustomContext, implement Toast

* put back syer's implementation

AndroidCompat/src/main/java/xyz/nulldev/androidcompat/androidimpl/CustomContext.java

@@ -50,10 +50,9 @@ import java.util.Map;
 /**
  * Custom context implementation.
  *
- * TODO Deal with packagemanager for extension sources
  */
 public class CustomContext extends Context implements DIAware {
-    private DI kodein;
+    private final DI kodein;
     public CustomContext() {
         this(KodeinGlobalHelper.kodein());
     }
@@ -734,4 +733,3 @@ public class CustomContext extends Context implements DIAware {
     }
 }
 
-