Implement the generator pattern in places where we handle big list

Implement the generator pattern in places where we handle big list: - [ ] [scaling] User list - [ ] [scaling] Iterating user list of a group - [ ] [perf] File list - For getChildren/getDirectoryContent merging the subsequent request is hard, especially for mount points with duplicates filenames. Solution would be to store the history of filesname with hash or something else. - Not so an issue for big instances as it is mostly one user having a lot of files in one folder. - [x] [scaling/perf] Add generator in IResult - [ ] Add documentation - [...