Use "origin" as remote name when initializing repositories

West does not use remotes in the Git repositories it creates, it always uses URLs for fetching. But it configures a remote for the user's convenience with the name of the remote attribute in the manifest.

In our manifest files we are currently using different remotes. And for our users it is cumbersome having to look up or having to remember the remote name of each project. Our workflow could be simplified if all the remotes are just named "origin". Also custom scripts could be made simpler if they don't have to look up the remote name first.

Please add an option to create all repositories with the remote name "origin" (or what Git's global config value clone.defaultRemoteName is set to).

This could also help #257