Makes local copies of all the linked images and pdfs in a post, adding them as gallery attachments.
Source & support:
https://github.com/ryanpcmcquen/import-external-attachments
This plugin is based on the work done in the “Import External Images” plugin by MartyThornley.
https://github.com/MartyThornley
HTTPS support added by IvanDoomer:
https://github.com/IvanDoomer
PDF support added by bengreeley:
https://github.com/bengreeley
Most of the JavaScript was rewritten from the original plugin, to reduce the
number of global variables.