Add event broker class
Add some sample brokers & new inputs
R plumbing
Fix so handlers now work
Allow handlers to be branch components
Clean up left_right example
Unname handler lists

This makes sure that the result isn't a named list with  for names.
Don't send functions to vega
Make it possible to add handlers with +
Handlers require a dynamic plot
Tweak left right defaults
Add keyboard handler JS code
Get correct id
Remove unused keyboard events
Tweak example
Merge branch 'events'