Updated documentation to allow personal folder browsing and analytics file deletion

FOR REVIEW ONLY

I have updated the descriptions for two endpoints (portal content browsing and file deletion) to handle the need to delete RBI files in a user's Personal Folder.  To accomplish this, I am proposing the following changes to current behavior:
*  the file deletion endpoint (`DELETE /accounts/${account_uid}/files/${file_uid}`) will allow deletion of analytics files (RBIs)
*  the portal contents endpoint (`GET /accounts/${account_uid}/portals/${portal_uid}/contents`) will allow browsing of Personal Folders (subject to specified security restrictions)

Please update this PR with comments / suggestions.  The goal is to drive the acceptance criteria for sprint tasks based on the changes in the documentation.