FEATURE: improved tag and category watching and tracking

- present tags watched on the user prefs page
- automatically watch or unwatch old topics based on watch status

New watching and tracking logic takes care of handling old topics
(either with or without read state)

When you watch a topic you now watch historically

Also removes confusing warnings from user.

spec/services/user_updater_spec.rb

@@ -39,6 +39,28 @@ describe UserUpdater do
       expect(user.reload.name).to eq 'Jim Tom'
     end
 
+    it 'can update categories and tags' do
+      category = Fabricate(:category)
+      tag = Fabricate(:tag)
+
+      user = Fabricate(:user)
+      updater = UserUpdater.new(acting_user, user)
+      updater.update(watched_tags: [tag.name], muted_category_ids: [category.id])
+
+      expect(TagUser.where(
+        user_id: user.id,
+        tag_id: tag.id,
+        notification_level: TagUser.notification_levels[:watching]
+      ).count).to eq(1)
+
+      expect(CategoryUser.where(
+        user_id: user.id,
+        category_id: category.id,
+        notification_level: CategoryUser.notification_levels[:muted]
+      ).count).to eq(1)
+
+    end
+
     it 'updates various fields' do
       user = Fabricate(:user)
       updater = UserUpdater.new(acting_user, user)