Added listFolderPermissions() in _services.py
Added listFolderPermissions() in _services.py

New function that lists principals which have permissions for the folder (goes into arcrest\manageags).
BrunoCaimar/ArcREST,adegwerth/ArcREST,Esri/ArcREST,DShokes/ArcREST,pLeBlanc93/ArcREST