Ideas for better offline use

`read_site_sheet` needs better error catching if the path is wrong. right now, if you give it the wrong path it tries to go to Dropbox anyway. This gives an unhelpful error and wastes time.

so just let it check, not for the existing file, but for being a certain length.

if it is long, must be a path, look for file

if file is absent exit with warning.
