style(*): add doc strings to deisctl and logger

This change quiets most `golint` warnings for the *deisctl/* and *logger/* components by adding go doc strings. It also removes several functions in the `deisctl/utils` package that were unused.

I would appreciate feedback on the accuracy and usefulness of the doc strings in particular.
In some doc strings we omit "for the Deis platform" and for some we don't. Was there a particular reason why some were omitted? Should we add this to other docstrings for consistency or remove it?