fixes #322 Ability to add custom variables and multiple values resovled
in a dynamic Hierarchally order

This commits introduces the ability to define variables per puppet
class.

additionally, each class can have multiple values, depends on the host
which is requesting that variable.
each variable, can have validations rules (such as regexp, pre definiend
list etc).
Each value is then evalutated against a matcher role, if not found, the
default value is returned.

as a follow up tickets, we would allow to edit values in the host form
( and host group, domain os etc)

an additional foreman setting was added, to define the default lookup
order (which can be overwritten per variable).