Fix #593 New option to ignore events by other workspace users in shared channels

[seratch]

Summary

This pull request fixes #593 by adding a new option named installedTeamOnly to configure Hubot not to react to other workspace users in a shared channel.

HUBOT_SLACK_TOKEN=xoxb-*** INSTALLED_TEAM_ONLY=true ./bin/hubot --adapter slack

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

Merging #597 into master will decrease coverage by 0.92%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master     #597      +/-   ##
==========================================
- Coverage   85.25%   84.32%   -0.93%     
==========================================
  Files           6        6              
  Lines         400      402       +2     
  Branches       88       90       +2     
==========================================
- Hits          341      339       -2     
- Misses         34       37       +3     
- Partials       25       26       +1     

Impacted Files	Coverage Δ
src/bot.coffee	73.10% <33.33%> (-2.96%)	⬇️

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