add map style setting

[RandomFractals]

to default map views to one of the supported mapbox/keplergl map styles.

see: https://github.com/keplergl/kepler.gl/blob/master/docs/user-guides/f-map-styles.md#map-styles.md

and: https://github.com/keplergl/kepler.gl/blob/master/src/constants/default-settings.js

[RandomFractals]

add custom map styles loading instead for default mapbox maps most devs are familiar with: streets, light, dark, outdoors, satellite and maybe monochrome ...

see: https://docs.mapbox.com/mapbox-gl-js/example/setstyle/

and this doc to override keplergl map style:

https://github.com/keplergl/kepler.gl/blob/master/docs/api-reference/advanced-usages/custom-mapbox-host.md#2-overriding-the-default-mapstyles

[RandomFractals]

quick preview pic of these new map style options ...