Post auth RTM start issue --closes #67 (#68) (#69)

Slack oauth flow #31 (#35) (#36)

* Registering multiple team using auth flow --wip #31

* Storing tokens in storage --wip #31

* Installing app working, api handler needs refactor to handle multiple tokens --wip #31

* Refactored api handler to use multiple tokens --closes #31

Merge branch 'master' of github.com:jacekelgda/vacation-status-update