Use PrimeIcons in generated menus

[ramrap]

Fixes #56

Summary

• import PrimeIcons in the generated layout component
• use PrimeIcons constants for the default generated menu icons
• use PrimeIcons.LIST when spiderly add-new-entity injects a menu item, adding the import when needed

Validation

• git diff --check
• static review of generated TypeScript import and menu item output

I could not run a local build in this environment because dotnet is not installed.

[filiptrivan]

@ramrap Sorry man please, but to contribute you need to follow contribution rules, I need to see tested app and some screenshots.