Implemented user setting for displaying allergens next to an offer

app/src/main/java/com/denizk0461/studip/viewmodel/SettingsViewModel.kt

@@ -0,0 +1,18 @@
+package com.denizk0461.studip.viewmodel
+
+import android.app.Application
+
+/**
+ * View model for [com.denizk0461.studip.fragment.SettingsFragment]
+ *
+ * @param app   reference to the app
+ */
+class SettingsViewModel(app: Application) : AppViewModel(app) {
+
+    /**
+     * This value determines whether the user wants to have allergens marked.
+     */
+    var preferenceAllergen: Boolean
+        get() = repo.getPreferenceAllergen()
+        set(value) { repo.setPreferenceAllergen(value) }
+}