Add mechanism to show that field was saved

[fregante]

For example:

• if _handleFormUpdates run successfully, add wos-saved class
• if _handleFormUpdates errors, add wos-error class and trigger an event named options-sync:error on the field
• when user starts typing, remove both classes

Invisible form auto-saving is great and "native", but feedback is good when things don't work well.

Maybe just the error needs to be handled.

[fregante]

When the save is successful, a options-sync:form-synced event is fired on the form