code format & remove unused code
Extra class for TodoCallback
Circuit Core extends GWT Core in order to suppress linker warnings in GWT Dev Mode
Introduce instance dependency between UserStore and TodoStore
Switch to org.bsc.maven:maven-processor-plugin:3.1.0-beta1 for annotation processing
Rename "ReceiveInfo" --> "ProcessInfo"
Remove unnecessary code
Simplify using EmptyAction as super-class
Remove blank line
Add documentation about the programming model