This fixes image links to /equation_images/X, among other things.
As part of this, I refactored the attachment.rb secure setting to be a
domain.yml (HostUrl) setting that can be used app-wide to determine
whether to use http or https when the code doesn't have access to a Request.
Fixes#8784
I also started down the road of having notification emails/sms/etc use
https links instead of http, but there is still work to do there, refs #9190
test plan: Use the rich text editor to post to a discussion or any other
rich text field that can be retrieved via the api, and include an
equation using the equation editor. Then retrieve that post through the
api, and verify that the url to the equation image includes the canvas
hostname and protocol (http://canvas.example.com/equation_images/X
instead of just /equation_images/X)
Change-Id: Iac28bf99d2d3b33c17d5b3eb128aa6d8488570fe
Reviewed-on: https://gerrit.instructure.com/11867
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Simon Williams <simon@instructure.com>
Brian Palmer