Additional administrative helper methods.

Added to admin.py:

updateServiceItemsThumbnail
registerItems
getFolderID
_getUserFolders
clearFolder
AGOLUserCatalog
AGOLCatalog
_getSize
_getOrgID
_getCatalogQuery

to support:
* samples/AGOLCat.py - Generate a CSV of items in a portal, optionally from a query or specific
folder.
* samples/clearFolder.py - Remove all items from a specific user folder.
* samples/registerItems.py - From a designated CSV list of MapService or Application URLs, register
the items to a portal, optionally to a specific folder.
* samples/updateServiceItemsThumbnail.py - For a portal or specific user folder, look for any blank thumbnails and
replace with a default version.