Kicking off new bug trackers (for a project) properly

This patch adds a new API option 'include_empty' to customs/api.py, for kicking off new trackers/projects when also specifying the 'just_stale' switch. So far, new projects had an empty bug list and wouldn't be included in the results...and therefore wouldn't get scraped for new bugs initially.

It might be nice to put parens around these URLs to make it a bit easier to read.