* enhancement: add graph beta listPermissions endpoint
besides the new api endpoint it includes several utilities to simplify the graph api development.
* resolve drive and item id from the request path
* generic pointer and value utilities
* space root detection
* update GetDriveAndItemIDParam signature to return a error
* move errorcode package
* enhancement: add generic error code handling
* fix: rebase
drives.go implemented a local user/group cache (ttl based) to speed up repeated
user and group lookups. This commit moves the implementation to the 'identity' module
to make it usable outside of drives.go.
