Documentation update

* Restructured index page
* Removed pure community stuff
* Created dynamodb_api dedicated document

Partially implements: bp magnetodb-documentation

Change-Id: Ifdebad11ae0466b4634a503ecb090d26d346774d
Validate get_item for presence of a range key

Raise ValidationError if table schema has a range key
and get_item request misses a value for the range key

Change-Id: Iff3d72f0539e503476feb1e7400242057abc2e3d
Fixes-bug: 1290878
Merge "Validate get_item for presence of a range key"