Add parameters as nodes to the visual graph

I'm working with multiple templates which import numerous values using [template parameters](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/parameters-section-structure.html). Currently the visual graph produced is quite flat and disjointed for most templates since their dependencies come from outside the template through the parameters. The visual would therefore provide a lot more usable information if the parameters and their connections to components which use said parameters would be displayed.

The issue names no repository files, tests, or entry points. Start by reviewing the linked CloudFormation parameter documentation and locating the visual graph generation flow; done means template parameters appear as graph nodes with connections to every component that uses them.

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