Track pending messages and add to history once confirmed
Track pending messages and add to history once confirmed

cpww/dale,slackhq/node-slack-client,slackapi/node-slack-sdk,paulcbetts/node-slack-client,peernohell/node-slack-client,slackhq/node-slack-sdk,slackapi/node-slack-sdk,DLavin23/dale,slackapi/node-slack-sdk,peernohell/node-slack-client,dshahin/node-slack-client,slackapi/node-slack-sdk,Shiggiddie/dale