Watchmaker

**Summary**:

* Documents configuration vs cli argument handling and precedence
* Provides a table mapping common scan findings to an associated Finding ID
* Restores propagation of the `None` value on the cli to the workers
* ash-linux-formula
- Ensures aide configuration complies with FIPS requirements
* ash-windows-formula
- Adds missing sls to restore support for Windows 10
* join-domain-formula
- Suppresses join-domain command in salt log output
- (Windows) Supports using salt-native pillar security for the `password` value
* nessus-agent-formula
- (Linux) Suppresses gpg verification so the pkg can be installed from a URL

**Summary**:

**Summary**:

* Add support for Windows Server 2019
* Use native markdown processing for PyPI long description
* Deprecate use of 'None' (string) in `config.yaml`
* Add optional `watchmaker_version` node to configuration
* Use Salt 2018.3.4 in default configuration

**Summary**:

* Pins `PyYAML` dependency when running on Python 3.4 or earlier

**Summary**:

* Uses CDN URLs for watchmaker config and content, instead of direct S3 URLs
* Pins `backoff` dependency when running on Python 3.4 or earlier

**Summary**:

* join-domain-formula
- Add support for restricting Active Directory sites that will be consulted if the `ad_site_name` key-value is set in the pillar
* ash-linux-formula
- Fix issue with log spamming by `systemd` related to file permissions
* ash-windows-formula
- Update STIG baselines for 2019-07 SCAP content
* scap-formula
- Rename DISA content files to reflect SCAP version
- Update DISA SCAP content to July 2019 release
* salt-content
- Update SCAP pillar to match filename changes in SCAP formula