* 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
* Implement POST /posts endpoint for APIv4
* Implement GET /channels/{channel_id}/posts endpoint for APIv4
* Implement GET /posts/{post_id} endpoint for APIv4
* Implement GET /posts/{post_id}/thread endpoint for APIv4
* Skip team get if it's a DM channel in handlePostEvents