added multiple event callbacks

[adumesny]

Description

• added event support to call grid.on('added removed change', callback)
  again even with native events (was jquery feature)
• updated demos to use it (like it!)
• fix for grid.on("added change removed", function(e, items) { ... }); not working: items is undefined #1171

Checklist

• Created tests which fail without the change (if possible)
• All tests passing (yarn test)
• [X Extended the README / documentation, if necessary