Add Slack slash commands support

[k2nr]

should be useful for all slack + barcelona users

[essa]

I have implemented a slash command from "Slack-echo-command" in following article.

• 【新機能】AWS LambdaにSlack連携のBluePrintが登場。ChatOpsがより手軽に ｜ Developers.IO

I think I can copy and modify it to implement a slash command for barcelona. It can use following APIs.

• AWS SDK
• Slack notification
• Any REST api

I'd like to implement /bcn deploy command like this.

/bcn deploy bluegreen-sensu -e staging

One thing remaining is "configuration files". My plan is putting them to a S3 bucket with following structure.

• S3 bucket ( <- This bucket name will be stored in somewhere in Lambda source )
  • bluegreen-sensu
  • barcelona.yml ( <- copy of the same file in repository )
  • barcelona-secret.yml ( <- encrypted, stores secrets like heritage-token )
  • bluegreen-consul
  • bluegreen-haproxy

All heritages have a directory of its name and two files in it. And they will be created by local bcn command just after the heritage was created.

@k2nr Could you comment about this plan and describe sub-commands you want to add briefly?