add geo assets so maps render without internet connection

[cpsievert]

No description provided.

[cpsievert]

@chriddyp we'll have to provide an explanation to CRAN as to why we need to include these assets...

* checking installed package size ... NOTE
  installed size is  5.5Mb
  sub-directories of 1Mb or more:
    htmlwidgets   5.0Mb

[cpsievert]

We'll have to wait a couple days to submit to CRAN, but feel free to merge @chriddyp

[chriddyp]

@cpsievert one issue that I've run into is that the geo assets make the bundle really large (5MB), which for some folks is too big for them to include into their shiny apps or their documents.

Plotly.plot will load the geo-assets asynchronously and on-demand (only when a *geo plot is made) from the CDN, but of course this requires an internet connection.

Is it possible for us to only load these extra assets with a config or call signature argument? Like geo_offline=true?

[cpsievert]

Hmm, it is certainly possible but might require a rather ugly hack.

[cpsievert]

Closing in favor of #411