allow longterm token to refresh

 - add config for duration of longterm key
 - move tokenDuration to helpers for better isolated testing
 - add better logging as to what is going on
 - refresh the longterm token for its original duration e.g. 90 days
correct name
set default config as 30 days
Merge pull request #9 from tidepool-org/jhbate/longterm-login

allow longterm token to refresh