Add events to contract explorer #1512

I propose the Lab display events that a contract has emitted in the contract explorer.

• Show events in Contract Spec
• Display contract's events from the RPC's getEvents endpoint
• Display contract events for a transaction

And, that it use the events spec available in the SEP-48 Contract Spec that's present in contracts built for protocol 23 onwards to render self-describing views of those events.

Today the contract explorer shows information about the contract executable, and its state, but not events:

See the following links for examples of how to combine raw contract events with contract specs for a user friendly view:

• [SEP-48] Contract Interface Spec: Events stellar-protocol#1724
• https://github.com/leighmcculloch/exp-sep48-derived-events-example
• Add self-describing events formats stellar-cli#2086