App improvements after 1st refactoring

[cedelavergne-ledger]

The proposed improvements are:

• Realaignment with latest Stax SDK (for easier keypad usage)
• Improve README for seed mode usage (to take this into account: https://github.com/LedgerHQ/app-openpgp/pull/68)
• Fix Historical Bytes Status Indicator value (https://github.com/LedgerHQ/app-openpgp/pull/75)
• Fix Historical Bytes buffer with correct padding (https://github.com/LedgerHQ/app-openpgp/issues/74)

Checklist

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

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 27.27%. Comparing base (91cdd1f) to head (db6242b).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #96 +/- ## ======================================== Coverage 27.27% 27.27% ======================================== Files 1 1 Lines 209 209 ======================================== Hits 57 57 Misses 152 152 ``` | [Flag](https://app.codecov.io/gh/LedgerHQ/app-openpgp/pull/96/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LedgerHQ) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/LedgerHQ/app-openpgp/pull/96/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LedgerHQ) | `27.27% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LedgerHQ#carryforward-flags-in-the-pull-request-comment) to find out more.

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