Add NavLink component to simplify links in headers/footers

[fwextensions]

• Taking the base URL into account when checking whether the current page is the same as one of the nav links is handled inside NavLink.astro.
• You can pass in a class prop to apply to the NavLink anchor.
• Add NavDropdown component to simplify the creation and styling of the header dropdown menus.
• Add header and footer tags inside the components.
• Fix the TypeScript errors.
• Adjust some of the styles to work with Pico v2.