Trigger should take arguments and environment variables

[pauldix]

When creating a trigger (a specific application of a plugin), it should take optional arguments or environment variables. A flat map should work where the key is the env variable name and the value is the default value to assign if the env variable isn't present.

When the plugin is triggered, these values should be passed to it for use.

This can be used to pass credentials, names of things to connect to, threshold values, and others.