Shiny re-design: building Leaflet map

[Pablo-source]

Using two newly created datasets LEAFLET_MAPS_DATA and METRICS_RATES_DATA, start re-designing main Shiny app file 03 ui_server_SHINY.R. In coming weeks the main app will be called 03 COVID_19_Shiny_app.R

This issue will focus on the initial Leaflet map design that will be placed on the top section of the shiny app.

[Pablo-source]

Completed initial POC Leaflet map, I will keep designing new features for this COVID-19 Shiny app in coming days