Create and show what's new dialog

app/src/main/java/org/futo/circles/MainActivity.kt

...o/circles/feature/explanation/CirclesExplanationDialog.kt

...java/org/futo/circles/feature/whats_new/WhatsNewDialog.kt

app/src/main/res/layout/dialog_circles_explanation.xml

app/src/main/res/layout/dialog_whats_new.xml

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

...ava/org/futo/circles/core/provider/PreferencesProvider.kt