Handle redirected comic URLs (duplicate imports)

[jackv24]

Is your feature request related to a problem? Please describe.
Sometimes when a user inputs a URL it is redirected, but the comic document name retains the original URL. This means that if someone else imports the comic using it's redirected URL directly the database will end up with two imports of the same comic.

Describe the solution you'd like
Importing should check the URL against existing comic doc names AND scrape URLs, and match to an existing comic if found.