allow for list of default git remotes in the settings file

rather than just one.

I have some repositories where the remote is "origin", others have "upstream". By making the setting `default_remote` accept both a single string or a list of strings, I can use it for either.
 
It will try them in order until one matches. The basic loop for this was already there, I just fixed the setting import and made it a list if it wasn't already one (single string case).