Theming improvements (#502)

* Split theme definitions into day and night

* Add support for Night Mode in code

* Add theme chooser in preferences

* Fix translations

* Adjust IDs

* Adjust preferences for custom themes

* UI tweaks for custom theme support

* Added code for custom theme support 🍅

* Fixed resource display in Kotlin 🍅

* Restored styles

* Updated strings

* Fixed getIdentifier() to fit into setTheme()

* Removed redundant resources

* Reset default theme to "Dusky"

* Fixed night mode handler to maintain compatibility

* Refactor functions to use helper methods

* Added license block

* Added preview to theme selector

* Added color identifier getter helper method

* Fixed reference in AccountMediaFragment

* Cleanup

* Fixed navbar foreground not changing color

* Fix fallback theme switch(){}

* Enable location-based daylight trigger

* Cleanup

* Modified theming strategy to reduce clutter in preferences

* Updated translations for latest version

* Removed "Default" theme flavor from settings

* Updated Polish translations 🇵🇱

* Modified TwilightManager handling code to support Android M's UiModeManager features and moved it to its own function

* Updated Polish translations 🇵🇱

* Cleanup; Fixed hardcoded string

* Added missing escape in string

* Removed permission request dialog.

As we now use native UiModeManager APIs that don't need special permission for Android 6.0 and above, we no longer need to bother user with Android M+ specific location permission request dialog.

* Increased readability of ThemeUtil class

* Refactored ThemeUtils.setAppNightMode method

* Cleanup

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

@@ -152,7 +152,6 @@
     <string name="pref_title_notification_filter_reblogs">mes pouets sont boostés.</string>
     <string name="pref_title_notification_filter_favourites">mes pouets sont mis en favoris.</string>
     <string name="pref_title_appearance_settings">Apparence</string>
-    <string name="pref_title_light_theme">Utiliser le thème clair.</string>
     <string name="pref_title_browser_settings">Navigateur</string>
     <string name="pref_title_custom_tabs">Utiliser le navigateur intégré.</string>
     <string name="pref_title_hide_follow_button">Masquer le bouton de suivi lors du défilement.</string>