[Polish] Second draft of DigiTransitSearchBox

[pingzing]

• [x] Make an empty searchbox only display "My Location" in the dropdown.
• [x] When the server returns nothing for a given collection, empty the collection.
• [x] Make favorites search-as-you-type, instead of always displaying all of them
• [x] Make the "Add Favorite" button behave as a "Toggle Favorite" button.
• [x] The REST endpoint for geocoding's search rectangle may not extend far enough north--investigate (edit: it does)
• [x] Display a little arrow at the bottom of the dropdown if it's scrollable and you're not at the bottom
• [x] ~Move progress bar into the textbox itself, so it's always visible~ Gonna scrap this one for now. More complicated than it's really worth.