[FR] Add "active search" indicator to Map UI

Setup

import fiftyone as fo
import fiftyone.zoo as foz

dataset = foz.load_zoo_dataset("quickstart-geo")
session = fo.launch_app(dataset)

Feature request

I think we should add some indicator to the Map tab whenever a selection has been made, to indicate to the user that they'll need to clear their selection in that component if they want to fully reset their view.

Possible ideas:

1. Make the tab orange (our "active" color)
2. Add a "notification"-style icon to the upper right of the tab element to show that a filter is active within it