#8355 OSHmail: add subheading

Add the text to the header image to ensure that it appears correctly in email clients
#8350 OSHmail handle YouTube videos

If a YouTube video is embedded in content in an OSHmail it will be
replaced with a link to the video on YouTube with a placeholder image
(taken from YouTube).
added protocol (https:) to the youtube URLs since several mail clients can't handle
the protocol-agnostic version. Refs #8350
remove 'is_default_page' from query inside sitemap - we don't seem to have that index in solr?? Fixes #8569
add More link to PRs #8342
Merge branch 'master' into oshmail-revamp
Merge branch 'master' into oshmail-revamp
Refs #9323 OSHMail revamp: add new collage layout to only show the title
Refs #9323 OSHMail revamp: update collage2table to only create one row
Refs #9323 OSHMail revamp: update oshamail template and CSS
#8350 OSHmail handle YouTube videos

If a YouTube video is embedded in content in an OSHmail it will be
replaced with a link to the video on YouTube with a placeholder image
(taken from YouTube).
(cherry picked from commit bb8d6d342f6d8404cc105525a94fadbede92314f)
Merge branch 'oshmail-revamp' of https://github.com/syslabcom/osha.theme into oshmail-revamp

Conflicts:
	src/osha/theme/cssselect.py
Merge branch 'master' into oshmail-revamp
Merge pull request #2 from syslabcom/oshmail-revamp

Oshmail revamp