Kind of fix for etalab tiles

[abulte]

This switches from data.map to a global var _map. The Etalab styles load successfully. There must be something left to adjust because layers don't show up, but it might be a good starting point.

PS: sorry for the huge diff but you have trailing spaces everywhere 😱 and my editor is configured to remove them. We should at some point (not right now) land on a common style guide / linter for javascript code. I like https://standardjs.com but airbnb or some other sane standard would be fine.

[JulienParis]

I succeded in fixing the bug + using the Etalab tiles thanks to your code : the global var _map is definitely working while putting the map object into the local data is not...

Meanwhile I added a lot of things to the mapboxGL component, + all the trailing spaces, so I'd prefer not merging this PR => cf #6

So the ES lintting will be for another PR, now that j_front is merged to master

That said the bug still in place after being able to use the Etalab tiles was because of some functions written under computed and had to be moved under methods ... If I remember it well