Notification List: Updates FSM states and placeholders

[bummytime]

This PR updates the FSM states on the notifications screen to now include emptyUnfiltered and emptyFiltered (just like Orders).

Now you will see the empty placeholder displayed if a given filter does not have corresponding notes (along with a button to remove the filter). The existing "no notifications" placeholder overlay displays when the filter == .all and the results are empty.

Fixes #542

Testing

1. Build and run the app. (Try to have only one kind of notification in your list)
2. Open the notifications tab

• Verify you see the notes

3. Select a filter (either orders or reviews) where there are no notes

• Verify you see the empty filter placeholder

4. Tap the "Remove filter" button in the placeholder

• Verify the filter is removed and you see all the notes again.

5. Select a filter (either orders or reviews) where there ARE notes

• Verify you see the notes

6. Select the all filter and then remove (trash all the notes)

• Verify you see "no notifications" placeholder

@jleandroperez would you mind doing a quick review?

[jleandroperez]

Looks great!!

[jleandroperez]

@bummytime sir, i'm hitting the button on your behalf, so that this one makes it in time for the code freeze!!