agent raises when no triggers are defined

[swerner]

if a user plans to trigger their agent manually, an error is raised:

gems/sublayer-0.2.3/lib/sublayer/agents/base.rb:45:in `setup_triggers': undefined method `each' for nil (NoMethodError)

        self.class.triggers.each do |trigger|

Two things planned here, one with no triggers defined it shouldn't error out, but we should also have a built in trigger subclass for manually triggering an agent