App storage use demonstrator

[iartemov-ledger]

Based on master...app-storage
Blocked by LedgerHQ/ledger-secure-sdk#865 or sooner a new PR targeting master
Pair review: LedgerHQ/app-security-key#69

Checklist

• No N_ variables anymore, only app_storage API
• defines accessor macros for READ and WRITE operations
• cached in RAM storage data use
• compile-time check for the data storage size
• 2 app storage versions demonstration
• backup and restore tested locally with app_storage_utils.py script
• current tests fixes:
  • Stax
  • Flex
  • NanoX
  • NanoSP
  • NanoS ?
• New --app-storage tests (requires support in Speculos, maybe a special test app needed)

• App update process has been followed
• Target branch is develop
• Application version has been bumped

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.46%. Comparing base (af99bcd) to head (31a21a2).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #147   +/-   ##
=======================================
  Coverage   88.46%   88.46%           
=======================================
  Files           5        5           
  Lines          78       78           
  Branches       20       20           
=======================================
  Hits           69       69           
  Misses          9        9           

Flag	Coverage Δ
unittests	88.46% <ø> (ø)

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