Custom JS event triggers/goals

Ability to fire JS triggers and see the number of times it fires within the dashboard. In addition, the ability to pass optional meta data and see this visibility. Bonus points for being able to optionally format the meta data in the dashboard, i.e. £/$/€/%, etc. Example code, that a developer can fire whenever a goal/event takes place: ```js IA.trackEvent('cart add', { _value: 100, // Value in cents }); ``` Use case: ability to track custom events means we can see better custom metrics. Similar to Fathom feature: https://usefathom.com/docs/features/events