[Finishes #55051018] Update toast library.

- Among style changes, shorten the toast length to 3s and hide notification on Backbone router navigate.
- To send an error toast use {toastOpts: {type:'error'}} as second argument.
- To change length in seconds use {toastOpts: {hideAfter:5}} - use 0 for 'sticky'
- Uses Messenger (https://github.com/HubSpot/messenger) via the messengerjs-rails gem (https://github.com/benjis/messengerjs-rails)
- MIT License