Add handlerType to constraints

[aoberoi]

Summary

Before this change when two handlers were registered for different kinds of requests (action and options), and an event was dispatched that met those constraints, the wrong handler could potentially be called. Since there was no way for the adapter to disqualify the first of the registered handlers, it would be selected, even if the payload for a different type of handler.

Also, the conditional checks done on the payload to determine if it was an action was incorrect. Dialog submissions do not have an actions property, so they were incorrectly treated as options requests.

Requirements (place an x in each [ ])

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

[codecov[bot]]

Codecov Report

Merging #40 into master will increase coverage by 0.01%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #40      +/-   ##
==========================================
+ Coverage   99.45%   99.47%   +0.01%     
==========================================
  Files           3        3              
  Lines         185      191       +6     
==========================================
+ Hits          184      190       +6     
  Misses          1        1

Impacted Files	Coverage Δ
src/adapter.js	99.28% <100%> (+0.03%)	:arrow_up:

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