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This now requires itemid, which cannot be null. This is safer. The
context can still be passed in as an optional parameter.

Previously we were sticky to 7.5.7 and this issue was
hitting our windows runs:

https://github.com/sebastianbergmann/phpunit/issues/3564

Get the latest post's author which takes into account private replies.

Update JS message drawer to allow delete message for all showing a new
checkbox in the confirm dialogue.

* moving course pattern generation to core_renderer

Also, added WS new return parameter candeletemessagesforallusers in get_conversation
and send_instant_message and added API support. This will be used to check
if the user can delete all messages in the conversation.