* PLT-1598 Slash command works in RHS
* fix UserProfile in the reply for Slash Command
* fix some problem about the system messages in RHS
* system message in RHS isn't displayed as comment for root message
* remove status indicator for system message in RHS
* system message in RHS is colored to grey
* system messages don't count as commented post
* fix bug about cleaning draft in RHS
* remove unnecessary function
* implement new model for executing command
