Automatically add an artist tag when fetching from Fur Affinity image direct link

[HushedFox]

Is your feature request related to a problem? Please describe.
The problem is that there is no fetching available from FA and also I sometimes forget to add artist tags when uploading from FA :P

Describe the solution you'd like
Direct links are always constructed like this:
https://d.facdn.net/art/username/somenumber/someothernumber.username_originalfilename.extension

Because name of the account is always present in direct links from FA in the same place it could be automatically added as a tag just like when fetching images from Twitter, so in the form of artist:usernamefromurl

One drawback exists for FA usernames that have the "_" symbol - it is omitted in the username in both profile url and direct links to art.

Another problem is that when uploading from account that is not the original artist the wrong tag will be added, but this problem exists also with fetching from Twitter. It could be resolved by implementing this: #47
, a checkbox that when unchecked would not fetch the artist tag.

Describe alternatives you've considered
This: #43 - a pop up that tells the user that they are trying to upload with no artist (origin) tags present