Give users option to include a list of data.frames in run_app()

[AARON-CLARK]

New argument could be called datalist. The user would simply have to bundle up their data like (below), but obviously use their own data sources. So, they could simply include a few lines in app.R to read them in. If the datalist argument is not NULL (the default), then we'd include the file browse widget, otherwise, we can can it. We'd have to write a bunch of checks to verify the user is loading something that makes sense.

datalist <- list(ADSL = tidyCDISC::adsl, ADVS = tidyCDISC::advs, ADAE = tidyCDISC::adae, ADLBC = tidyCDISC::adlbc)

Somewhat related to #91.

[AARON-CLARK]

Per discussion on 4/20, maybe leverage a config file!