Add new Theme "Use System Design" + fixes to night mode (#1069)

* Add theme system

A theme which follows system design.
See: https://www.xda-developers.com/samsung-galaxy-s9-update-night-mode-schedule/

* update

to be in line with https://github.com/tuskyapp/Tusky/pull/1060/files

* Update ThemeUtils.java

* update

* Cleanup

* Update Deps

* Cleanup

* Update PreferencesActivity.kt

* Workaround to make MODE_NIGHT_FOLLOW_SYSTEM work

* Update ThemeUtils.java

* Use ThemeUtils.THEME_SYSTEM

* Update SplashActivity.kt

* Update strings.xml

* Update Deps

* Update build.gradle

* Update build.gradle

* fix tests

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

@@ -205,6 +205,7 @@
         <item>Light</item>
         <item>Black</item>
         <item>Automatic at sunset</item>
+        <item>Use System Design</item>
     </string-array>
 
     <string name="pref_title_browser_settings">Browser</string>