[WIP] Frontend improvements

[qgustavor]

Implementing some ideas from #15. A short summary of the changes:

• Started working from the changes from guilhermearmelo (#39)
• Changed webpage title from "Layers Control Tutorial - Leaflet" to "Brumadinho Location"
• Opinionated cleanup and reworking of the HTML and JavaScript
• Replaced omnivore library and area_quente.kml by hot_area.json as GeoJSON which can be handled directly by Leaflet
• Replaced document.getElementById and onclick with Vue
• Added a navigation bar and a simple explication text
• Started working on multiple language support

A screenshot:

I avoided drastically changing the code so I think people who already worked with it can still understand it. Some suggestions?