Users can browse and manage custom sample Lambda events to use as starting points for input into their Lambda handlers

[mpiroc]

Lambda invocations require a JSON "event". You can find sample events for AWS services in the public docs, but users might want to define their own sample events.

• Create a "Sample Lambda Event Manager" view, and add it to the AWS viewCollection
• event manager tree would have two top level nodes: "Curated Events", and "Custom Events". This issue deals with the latter (Users can browse sample Lambda events to use as starting points for input into their Lambda handlers #106 deals with the former)
• each node under Custom Events represents a single event that a user has created and can manage
• each custom event has a name and optional description, which will be surfaced in selection pickers
• All custom events are backed by a single json file that resides in the workspace. UX gestures to modify the file ultimately end up opening this file in an editor for the user to work with
• custom events can be added, edited, and deleted (hook up to context menus appropriately)

Later on, when we have the ability to Run/Debug Lambda Handlers locally, these events will be referenced as options to pass into the handler.

[justinmk3]

merged w/ #106