enable single config file support

[zilchms]

Fixes some parts of #158 .
Defines the openssl::config type which handles exactly one config file per resource instantiation.
Changes the openss::configs class to use the new type.

Allows other modules to instantiate a config file as follows:

openssl::config {'/path/to/config':
  ensure     => 'present',
  commonname => 'somewhere.org'
}

[bastelfreak]

for all the string parameters, please check if empty strings make sense, otherwise switch to String[1]