KVStore & derived classes: design docs, implementation & configuration

Implement the following:
KVStore base class
TDBStore class
FileSystemStore class
SecureStore class
Global APIs
Configuration framework
Design documentation

Author: David Saada

docs/.gitignore

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docs/design-documents/features/storage/Configuration/CONFIGURATION.md

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docs/design-documents/features/storage/Configuration/FILESYSTEM.jpg

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docs/design-documents/features/storage/Configuration/FILESYSTEM.xml

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