Add a rule for validating modules

Problem/Motivation

Right now there is a rule to disallow installation of specific modules. I'd like to do a little more than that with a rule. I'd like to specify modules that should generate a warning but should not be disallowed from installation.

Proposed resolution

Change up the existing disallowed module rule to support 'advisory' modules, where caution is advised. In order to provide more information on why a module is marked as having an 'advisory' an option can be added to the rule that displays an informative message.

Remaining tasks

None

User interface changes

Displays the message if given to the user, in both the drush command and form interface.

API changes

Removal of the ModulesDisallowedRule in favour of a new ModuleValidation rule.

Data model changes

New config for the ModuleValidation rule.