* image proxy support
* go vet fix, remove mistakenly added coverage file
* fix test compile error
* add validation to config settings and documentation to model functions
* add message_source field to post
* Option to add user to channel if mentioned user is not currently in the channel
* instead of link from server, just add component on client side to add channel member
* change implementation using post.props
* do clean up and add test
* sanitize post.props['add_channel_member'] on post creation
* move sanitize to app.CreatePost and also apply to app.UpdatePost
* Revert "PLT-6603: Don't return all posts on invalid query. (#7061)"
This reverts commit 25a2013890.
* Revert " #4755 Combining consecutive user join/leave system messages to single message and few other changes. (#5945)"
This reverts commit 8a91235fb3.
