adding portable code

Hi Julie,

Trying out a pull request to include this portable code. Hope this is relatively painless. You should only have to accept this pull request to transfer updated files.

I just committed a little common.R file as part of this [ohiprep commit](https://github.com/OHI-Science/ohiprep/commit/7ec50f0561418fd5393d09fd6a8cd0d74920a6b9#diff-207250adc66b4fa693f7f5f61f7da5a8R6).

As an example, notice lines 6-24 Global/NCEAS-Regions_v2014/ingest_checks.R, especially  `source(common.R)` and use of `file.path(dir_neptune, ...)` .

Eventually, we'll probably want to make this a dedicated R package so we can have well documented functions. When we do that the folder paths and code for manipulating paths will probably also change.

BB

PS Sending this to Melanie too.