Use module level exportation in box

[caldwellst]

As referenced in #211, should implement functionality more like this.

utils/init.R

#' @exports
box::use(src/utils/cloud_storage)
box::use(src/utils/location_codes)

So just like Python. My idea would be to use current folder structure to have those init files. Then we would just have to do:

box::use(src/utils)

utils$read_az_file() # from cloud_storage.R
utils$function() # any other function in modules in utils