[Inbox] Option to Preview and Save a Message before sending

[DeteesWuber]

Problem statement:

Currently, I can either send a message immediately - as it is - from the Canvas Inbox or cancel the message. I cannot prepare a message and then Preview it first. Many teachers don't realize that URL are actually displayed as hyperlinks and also also - the editor right now isn't a wysiwyg editor - the message may look quite different with e.g. attachments and media embeds.

Proposed solution:

Allows users to preview the message so they can decide if everything is OK and send the message as is, edit it, or discard it.

User role(s):

admin,instructor,student,ta