Corrections to UsersModule templates

Correct classname in the Users Module templates where aliases don't work (e.g. `UsersModule\Constant` -> `Zikula\Module\UsersModule\Constant`). Correct usage of `|const` modifier (was being used as `|constant` which is not available in the core as far as I can see.
Merge pull request #793 from craigh/UserModuleFix

Corrections to UsersModule templates