Combine Sharepoint with OneDrive and address feedback from review per…

…iod (cisagov#393)

* draft update & merge of Sharepoint OneDrive

* fixed policies wrong spelling

* fixed note indent formatting

* delete onedrive md file - have a combined file now

* missing heading for some implementations

* Added rationales for all policy items.

* spelling errors and removed instructions comma

* changed IDs to SHAREPOINT based on team vote

* fixed duplicate ID in instructions

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Co-authored-by: Addam Schroll <aschroll@mitre.org>