Reworked import processing to allow passing id=all to the GET query
instead of a numeric Repo ID.  With this argument, the system will
automatically run the "import latest" for all repositories configured
for source integration.  This will simplify the process for keeping a
large number of repositories up to date via cron job.

Cleaned out output from repository import to look nicer, and support an
eventual UI option to import latest from all repos.