Update UML documentation for PcCoarsen

[WorkGitAccount]

References #12 and #18

The current diagram does not follow strict UML guidelines and instead focuses on flow of data and steps of execution.

As a developer, I need a more in-depth UML diagram of the PcCoarsen class and its dependencies.

• [ ] PcCoarsen class documented with datatypes and functions
• [ ] Simplify where needed and focus on PcCoarsen and essential dependencies

[WorkGitAccount]

Walked through the relevant code. Made another PlantUML diagram isolating only PcCoarsen and direct dependencies.

[t:45]

[WorkGitAccount]

Updated how PcCoarsen interfaces with matlab. Added data types and variables where needed. Verified all dependencies are shown.

[t:30]