Add an option to change the current address

[guytepper]

Give the user an option to change their current address after they gave their initial coordinates in the intro modal.
Lots of users requested this feature to see protests in other location, and it also provides a solution to #5.

Ideally this should be a search box just above the ProtestList:

Most of the work will probably done inside App.js:

• The protests displayed on the ProtestList are stored inside the protests state property. Note that they are loaded only initially, so it will need to be changed.
• userCoordinates state property (which resembles the initial user coordinates, and stay the same even as they move the map) should be updated with the new coordinates.
• PlacesAutocomplete can be used to provide suggestions & geocode values.