Update to fetch the new _raw resolution

[nonamethanks]

As of a couple of weeks ago, tumblr now also serves the full untouched pictures as they were uploaded.
Example:

https://68.media.tumblr.com/ff834e2297be5c3d396cc36a26c72553/tumblr_o8aju9wTMZ1sl8albo3_raw.png
https://68.media.tumblr.com/e27ad63f314f1ffe3e5d07731c22ddbf/tumblr_obxybpdDJy1vxgw0io1_raw.png
https://68.media.tumblr.com/2748accb2245230b545b97967a947de2/tumblr_obr57xOlpY1vxgw0io1_raw.png

You'll notice from those two pictures that there's no limit in resolution anymore.

The _raw pictures are not offered by the API, they can only be fetched by changing each url's number from _1280 or whatever to _raw, and it does not work for files uploaded before 2013 - and this is not consistent, so the program should try to fetch the _raw file first and then fall back to the 1280 version if it fails.