Interactive option to select directories if datadir/outputdir are not provided or do not exist

[jhmigueles]

Is your feature request related to a problem? Please describe.
For new R users, the first challenge they find is usually the definition of the directories. It may be frustrating for them not being able to use GGIR just because of this.

Describe the solution you'd like
I think providing the opportunity to interactively choose files/directories with utils::choose.files and utils::choose.dir would facilitate the introduction to GGIR. But I'm not sure if this should be extended for the definition of the log paths (sleeplog, activity log, data cleaning file...).

[vincentvanhees]

Document in vignettes/github.io how to use

datadir = utils::choose.dir()
# OR
datadir = "C:/folder/data"

GGIR(data = datadir, ...)

Older ideas:

1. As described above with pop-up window to select path. => for inspiration see also: https://github.com/vincentvanhees/ActChronicFatigue Ideally we should avoid adding new dependencies
2. Document better how to specify paths.