switch transparency to overlay theme

src/main/java/com/owncloud/android/ui/preview/PreviewImageActivity.java

@@ -123,12 +123,6 @@ public class PreviewImageActivity extends FileActivity implements
                         }
                     }
                 });
-
-        // Add transparency to bottom navigation bar where supported
-        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
-            getWindow().setFlags(WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS,
-                    WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS);
-        }
          
         if (savedInstanceState != null) {
             mRequestWaitingForBinder = savedInstanceState.getBoolean(KEY_WAITING_FOR_BINDER);

src/main/res/values-v19/styles.xml

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+
+    <style name="Theme.ownCloud.Overlay" parent="style/Theme.ownCloud">
+        <item name="android:actionBarStyle">@style/Theme.ownCloud.Overlay.ActionBar</item>
+        <item name="android:windowActionBarOverlay">true</item>
+        <item name="android:windowFullscreen">true</item>
+        <item name="android:windowTranslucentStatus">true</item>
+        <item name="android:windowTranslucentNavigation">true</item>
+        <!-- Support library compatibility -->
+        <item name="actionBarStyle">@style/Theme.ownCloud.Overlay.ActionBar</item>
+        <item name="windowActionBarOverlay">true</item>
+    </style>
+</resources>