Split requests made by Danbooru::Http into either internal or external
requests. Internal requests are API calls to internal services run by
Danbooru. External requests are requests to external websites, for
example fetching sources or downloading files. External requests may use
a HTTP proxy if one is configured. Internal requests don't.
Fixes a few source extractors not using the HTTP proxy for certain API calls.
Add support for uploading posts from Gelbooru. Note that the translated
tags will include both the Gelbooru tags and the tags from the Gelbooru
post's source. The commentary and artist information will also be taken
from the Gelbooru post's source. The source of the Danbooru post however
will be left as the Gelbooru post itself, not as the Gelbooru post's source.
Don't show deprecated tags in the related tags or translated tags lists
when editing a post. It doesn't make sense to recommended adding tags
that can't be added to the post.
