manage user/groups separately

[igalic]

We like to manage our users centrally, and would like to do that will puppetboard's user also

[nibalizer]

@igalic would manage_user and manage_group parameters to the main class be sufficient to you? Default to true, but you could override them to false?

[igalic]

@nibalizer I was going to provide a pr with exactly that, but got stuck yak shaving something else ;)

Patch coming up, soon.