Make commands asynchronous by default

[chancancode]

We want to change the semantics so that commands and interactions are executed synchronously (as opposed to putting it in a queue) by default. It should still be possible to opt into the current asynchronous behavior with something like this:

class MonkeyCommand < Slackathon::Command
  async def call
    {
      response_type: "ephemeral",
      attachments: [{
        callback_id: "monkey",
        text: "Please pick a style",
        actions: [{
          type: "button",
          text: "Click to use :see_no_evil:",
          name: "post_in_channel",
          value: "#{params[:text]} :see_no_evil:"
        }, {
          type: "button",
          text: "Click to use :hear_no_evil:",
          name: "post_in_channel",
          value: "#{params[:text]} :hear_no_evil:"
        }, {
          type: "button",
          text: "Click to use :speak_no_evil:",
          name: "post_in_channel",
          value: "#{params[:text]} :speak_no_evil:"
        }]
      }]
    }
  end

  async def post_in_channel(value)
    {
      response_type: "in_channel",
      delete_original: true,
      text: "<@#{params[:user][:id]}> said #{value}"
    }
  end
end

The async class method can store the symbols in an array on the class instance, and dispatch_* can check whether it should call the method synchronously.