[mobile & web] Add option to change the theme

There are multiple ways to change a theme. The easiest might be to update the basemap using [toggleBaseMap].
However, if you are not using `Basemap`s you are forced to update the style of your VectorTileLayer.

Based on the Platform we might have to do different things:

#### JS:
There is an API to update the style of the current layer. This style can be a url or an object containing the style definition. This is handy when switching styles offline.
https://developers.arcgis.com/javascript/3/jsapi/vectortilelayer-amd.html#setstyle

#### Android:
Still looking into the possible ways..

#### iOS:
Still looking into the possible ways..