Use Geolocation API to center map by current location on load in certain cases

[mwpark2014]

See #192

This is

v0: If they already have location services allowed AND if there's no pos/zoom hash in the url, use Geolocation API to center map

Unfortunately, it appears that checking if a user has already given location permissions is only possible through an async promise. Therefore, the options are either making the map load wait until we can pass in user's geo coords or recentering the map after the mapBox object has been created.
In my approach, I try to kick off the permissions query asap. Inside a useEffect hook, we recenter the map as soon as the permissions query promise resolves and there is a map object in state. This is not guaranteed to run before mapboxMap kicks off its load event.

Assumptions:

• This app only supports modern browsers due to support for the Permissions API: https://caniuse.com/permissions-api
• This code is only ran client-side so we don't run into any node shenanigans

Manually Tested:

• User does not get prompted for location permissions
• If there is a hash coordinate already present, map will not recenter
• If user does have permissions and there is no existing hash coord, map will load up centered at user's location

[mwpark2014]

Closing since this issue is being replaced by:

1. Fallback to ipstack if user has not enabled geolocation permissions to allow map to center on user's location on load #392 for first time users
2. Save user's params in local storage and load them by default on load #447 for repeat users