Revert "Rename APIUtil as AppManagerUtil."

This reverts commit bc0faea2a4322d0605d2823bd319889109a0134e.
Merge branch 'master' of https://github.com/wso2/app-manager
Merge branch 'master' of https://github.com/wso2/app-manager
Merge branch 'master' of https://github.com/wso2/app-manager
Merge branch 'master' of https://github.com/wso2/app-manager
Fixing date calculation issue.