Adding A toggle for the dark theme.

app/src/main/res/values/strings.xml

@@ -17,6 +17,7 @@
     <string name="title_turn_off_rotation">Turn off rotation</string>
     <string name="title_notification">Notifications</string>
     <string name="title_turn_off_vibrations">Turn off vibrations</string>
+    <string name="title_dark_theme">Dark theme</string>
     <string-array name="entries_list_view_information_preference">
         <item>Both</item>
         <item>Only for open Facilities</item>

app/src/main/res/xml/settings.xml

@@ -17,6 +17,12 @@
             android:entries="@array/entries_list_view_default_tab_preference"
             android:entryValues="@array/entryvalues_list_view_default_tab_preference" />
 
+        <SwitchPreference
+            android:defaultValue="true"
+            android:key="dark_theme"
+            android:title="@string/title_dark_theme"
+            android:entries="@array/entries_list_view_default_tab_preference"
+            android:entryValues="@array/entryvalues_list_view_default_tab_preference" />
     </PreferenceCategory>
 
     <PreferenceCategory