Fixed cleaning the package info dict for schema 2.0+
Added support for the "sublime_text" key in a release to be "*" for matching all versions
Fixed the RepositoryProvider to always provide the "last_modified" key
Added a new "sources" key to the dict coming out of the providers, primarily to allow for webhook notification of repository updates
Added a way to limit what URLs the providers try to access, for the purpose of doing small, targetted updates