Check up front that we have all the packages required for our formats.

[wlandau]

Prework

• Read and abide by drake's code of conduct.
• Search for duplicates among the existing issues, both open and closed.

Description

If we use drake_plan(x = target(your_df(), format = "fst") and the fst package is not installed, drake throws an error at the last minute. We should check ASAP that all the packages are present for the selected formats. We should also emphasize in the docs that these packages do not come pre-installed with drake.

cc @MilesMcBain

[wlandau]

Related: ropensci-books/drake#145

[wlandau]

Turns out this patch makes vis_drake_graph() and friends brittle. I think those utility functions should work without formats, so I am putting this check at the very beginning of make() instead of drake_config().