Moving slash-commands out of app package (#14979)

* Moving slash-commands out of app package

* Fixing golint checks

* Fixing golangci-lint

* Fixing golangci-lint errors

app/plugin_commands.go

@@ -141,11 +141,11 @@ func (a *App) tryExecutePluginCommand(args *model.CommandArgs) (*model.Command,
 		return matched.Command, nil, model.NewAppError("ExecutePluginCommand", "model.plugin_command.error.app_error", nil, "err="+err.Error(), http.StatusInternalServerError)
 	}
 
-	for username, userId := range a.mentionsToTeamMembers(args.Command, args.TeamId) {
+	for username, userId := range a.MentionsToTeamMembers(args.Command, args.TeamId) {
 		args.AddUserMention(username, userId)
 	}
 
-	for channelName, channelId := range a.mentionsToPublicChannels(args.Command, args.TeamId) {
+	for channelName, channelId := range a.MentionsToPublicChannels(args.Command, args.TeamId) {
 		args.AddChannelMention(channelName, channelId)
 	}