Fixed theme

- fixed: currentMode, dark, light now actually emit new values when changed
- added: getters for lightTheme, darkTheme, and systemTheme
- breaking: currentMode -> systemTheme
- added: currentTheme
- breaking: currentMode => currentTheme
- change: Arcane.theme.followSystemTheme(context) required to follow system theme
- change: After following the system theme, calling Arcane.theme.switchTheme() cancels following the system theme
- added: ArcaneReactiveTheme is now registered in ArcaneServiceProvider when using ArcaneApp

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>

example/lib/main.dart

@@ -61,7 +61,7 @@ class _MainAppState extends State<MainApp> {
         debugShowCheckedModeBanner: false,
         theme: Arcane.theme.light,
         darkTheme: Arcane.theme.dark,
-        themeMode: Arcane.theme.currentMode,
+        themeMode: Arcane.theme.currentTheme,
         home: Scaffold(
           appBar: AppBar(
             title: const Text("Arcane Framework Example"),