Handle common issues on import

[slaporte]

When a coordinator imports files, Montage should:

• warn about deleted files #30
• resolve moved files #97
• resolve full Wikimedia Commons URLs
• resolve URL encoding issues
• resolve common typos (spaces or underscores at the beginning or end of the filename)
• warn users when files are not imported #108
• save a log of files that were not imported #108
• provide an easy tool to figure out which files from your source list are not in the round #140
• ensure there are no duplicate entry errors #146