Added handling of wikis that have been removed

  Previously the wikis that we have on disk were attempted to be fetched
  regardless of if the wiki was avaliable or not so now we do an explicit
  check to ensure that in the case of a deleted wiki, we do not break the
  whole process.

  Edit: Same fetch check has been added to source repos as well
Merge pull request #9 from sgnn7/removed_wiki_handling

Added handling of wikis that have been removed