Cw 373 theme refactoring in preparation to support additional themes (#933)

* refactor(Theme): migrate accentColor

- based on the specs at https://docs.flutter.dev/release/breaking-changes/theme-data-accent-properties#migration-guide.

* refactor(Theme): all deprecated TextTheme styles

* refactor(Theme): deprecated backgroundColor for colorScheme.background

* refactor(Theme): deprecated buttonColor to use TextTheme backgroundColor instead

* refactor(Theme): deprecated isAlwaysShown to use thumbVisibility instead

lib/src/screens/support/support_page.dart

@@ -19,7 +19,10 @@ class SupportPage extends BasePage {
 
   @override
   Widget body(BuildContext context) {
-    final iconColor = Theme.of(context).accentTextTheme!.headline1!.backgroundColor!;
+    final iconColor = Theme.of(context)
+        .accentTextTheme!
+        .displayLarge!
+        .backgroundColor!;
     // FIX-ME: Added `context` it was not used here before, maby bug ?
     return Center(
       child: ConstrainedBox(