Refactor url path names for DRYness

[echappen]

Currently, we enter path names throughout the site as interpolated strings.

Example:

<Link href={`/orgs/${params.orgId}/users`}...

This means when a path name needs to be updated, we need to find + replace every instance.

Create a pathname helper (or find an npm package for this) that enables us to update path names in one place.

Acceptance Criteria

• url pathnames are updated in one place
• components now use url pathname helper for links