Update several files for using CI 3.0

That is, replace constant "EXT" with "'.php'"
Merge branch 'feature/app-cores' into develop
Merge branch 'develop' into feature/acl
Fix bug in Template::_ext: Add period before "php"
Update core Admin_Controller to use new Template-lib methods
Update ctlr users/_admin/login to new template lib
Merge branch 'develop' into feature/acl