New utils/facts.py: Provide facts about the repo like role and module lists

The list of modules and roles is needed in several scripts now,
therefore it makes sense to have one place for this.

Here are the current variables:

BASE_DIR:           Base directory of the repo
ROLES:              List of roles in the roles folder
MANAGEMENT_MODULES: List of management modules in the plugins/modules
                    folder
ROLES_MODULES:      List of modules in the roles/*/library folders
ALL_MODULES:        List of all modules, the management and the roles
                    modules

All lists are sorted.