Set navigation bar color to dark on dark theme (#3091)

Wiktor created

* Allow overriding ConversationsTheme.Dark

This change splits the dark theme style into two styles - base that
stays the same in all configurations and Dark - the original - that can
be overridden in specific configurations to add version specific styles.

* Set navigation bar color to dark on dark theme

Use secondary background color as navigation bar color when using dark
theme. This avoids mismatched white colors on certain system themes.

Change summary

src/main/res/values-v21/themes.xml | 6 ++++++
src/main/res/values/themes.xml     | 4 +++-
2 files changed, 9 insertions(+), 1 deletion(-)

Detailed changes

src/main/res/values-v21/themes.xml 🔗

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <style name="ConversationsTheme.Dark" parent="ConversationsTheme.Dark.Base">
+        <item name="android:navigationBarColor">@color/grey900</item>
+    </style>
+</resources>

src/main/res/values/themes.xml 🔗

@@ -99,7 +99,9 @@
         <item type="reference" name="icon_enable_undecided_device">@drawable/ic_new_releases_black_24dp</item>
     </style>
 
-    <style name="ConversationsTheme.Dark" parent="Theme.AppCompat.NoActionBar">
+    <style name="ConversationsTheme.Dark" parent="ConversationsTheme.Dark.Base" />
+
+    <style name="ConversationsTheme.Dark.Base" parent="Theme.AppCompat.NoActionBar">
         <item name="colorPrimary">@color/green800</item>
         <item name="colorPrimaryDark">@color/green900</item>
         <item name="colorAccent">@color/blue_a100</item>