Added more to FileHelper

added GetFileById

Also implemented trivial methods
Implement GetFilebyId

Trivial, sample from the Goog
Implemented HasChildren, GetSiblings

More short methods
Also changed some return types to be Collection instead of ArrayList
Merge remote-tracking branch 'origin' into grdaneault
Merge pull request #12 from RITHonorsTechCommittee/grdaneault

Improved FileHelper and FileHelperImpl