[GHG-654] Added mentions on sidebar buttons / rhs bar#775

cyrusjc wants to merge 4 commits intomattermost:mastermattermost/mattermost-plugin-github:masterfrom

cyrusjc:cyrusjc/adding-mentions-to-sidebarcyrusjc/mattermost-plugin-github:cyrusjc/adding-mentions-to-sidebarCopy head branch name to clipboard