Use dark navigation bar in QR scanner activity (#3551)

Wiktor Kwapisiewicz created 

* Use dark navigation bar on dark theme

This approach uses `tools:targetApi` instead of separate theme file and
avoids lint errors.

* Use dark navigation bar in QR scanner activity

This is consistent with the black background that is already used in
that activity.

Change summary

src/main/res/values-v21/themes.xml | 6 ------
src/main/res/values/themes.xml     | 8 ++++----
2 files changed, 4 insertions(+), 10 deletions(-)

Detailed changes

src/main/res/values-v21/themes.xml 🔗 

@@ -1,6 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<resources>
-    <style name="ConversationsTheme.Dark" parent="ConversationsTheme.Dark.Base">
-        <item name="android:navigationBarColor">@color/black</item>
-    </style>
-</resources>

src/main/res/values/themes.xml 🔗 

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<resources>
+<resources xmlns:tools="http://schemas.android.com/tools">
 
     <style name="ConversationsTheme" parent="Theme.AppCompat.Light.NoActionBar">
         <item name="colorPrimary">@color/green600</item>
@@ -114,13 +114,12 @@
         <item type="reference" name="icon_enable_undecided_device">@drawable/ic_new_releases_black_24dp</item>
     </style>
 
-    <style name="ConversationsTheme.Dark" parent="ConversationsTheme.Dark.Base" />
-
-    <style name="ConversationsTheme.Dark.Base" parent="Theme.AppCompat.NoActionBar">
+    <style name="ConversationsTheme.Dark" parent="Theme.AppCompat.NoActionBar">
         <item name="colorPrimary">@color/green800</item>
         <item name="colorPrimaryDark">@color/green900</item>
         <item name="colorAccent">@color/blue_a100</item>
         <item name="popupOverlayStyle">@style/ThemeOverlay.AppCompat.Dark</item>
+        <item name="android:navigationBarColor" tools:targetApi="21">@color/black</item>
 
         <item name="color_background_primary">@color/grey800</item>
         <item name="color_background_secondary">@color/grey900</item>
@@ -281,6 +280,7 @@
         <item name="android:windowFullscreen">true</item>
         <item name="android:windowContentOverlay">@null</item>
         <item name="android:windowBackground">@android:color/black</item>
+        <item name="android:navigationBarColor" tools:targetApi="21">@color/black</item>
     </style>
 
     <style name="SplashTheme" parent="Theme.AppCompat.NoActionBar">