Update app : features, UI, tests, CI.

[agrojean-ledger]

Update the boilerplate so it has the same features as the C boilerplate (https://github.com/LedgerHQ/app-boilerplate) :

• Use new UI gadgets to have richer and more standard main menus.
• Implement standard command processing (get pubkey, sign tx, get app name, get version...) with display when necessary.
• Add Ragger functional tests (same as the C boilerplate).

⚠️ The nanos-ui PR has to be merged first : LedgerHQ/ledger-device-rust-sdk#95

ℹ️ there is no "app state" management implemented as in the C app. Why ? Because I forgot.

[yogh333]

LGTM, except for Cargo.toml (did not perform a deep review of the sources TBH...)

[yogh333]

👌