Adapt to Leaflet > 1.0.3

[IvanSanchez]

The master branch in Leaflet now uses a ES6 module structure, changing a lot of the internal calls to e.g. L.DomEvent.* → DomEvent.*.

Code for the rotate functionality should be adapted/rebased so it can be merged on top of that.

[MariusAlch]

That would be nice

[sisou]

@IvanSanchez I am happy to start adapting the rotate code. How would you suggest we best do it? Go commit by commit and adapt? Was the change to ES6 structure a single merge commit or was it done over time and multiple commits? Should we first rebase on top of the last "ES5" snapshot and then adapt to ES6?

I believe it will be quite some effort still :D