Refactor and migrate more functions out of api into app package (#5063)

app/preference.go

@@ -0,0 +1,16 @@
+// Copyright (c) 2016 Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package app
+
+import (
+	"github.com/mattermost/platform/model"
+)
+
+func GetPreferencesForUser(userId string) (model.Preferences, *model.AppError) {
+	if result := <-Srv.Store.Preference().GetAll(userId); result.Err != nil {
+		return nil, result.Err
+	} else {
+		return result.Data.(model.Preferences), nil
+	}
+}