[web-client] Make graph abstraction layer useful

[JammingBen]

The web-client package follows the paradigm of providing an abstraction layer between the server and a (web-) application that converts API data into objects with helpful types and utilities. This ensures that users of the server APIs don't need in-depth knowledge about them.

However, the Graph layer is currently an exception to this as it doesn't process any data returned by the server. We want to change that so it aligns with the other layers.

Acceptance criteria

• Split up the index.ts file into separate factories (similar to the WebDAV implementation)
• Drives are being returned as SpaceResource
• Drive items and their permissions are being returned as OutgoingShareResource or IncomingShareResource
• Permissions are being returned as Share
• Think about a convenient way to provide options such as filters