Use the new api definitions in all api calls.

Note that the `apigetfile` did some weird things to convert old-style
plotlyjs figures (e.g. `type: ‘histogramx’`) to new-style versions.

I wanted to ween us off the old api, so this makes the change from
`/apigetfile` —> `/v2/plots/[fid]/content?inline_data=true`.

The `_swap*` functionality was copied from `plotly/streambed` code,
directly from the backend’s implementation of `apigetfile`.

Author: theengineear