Add SDCard and Smartcard support for key storage

[stepansnigirev]

Flexible security model that you can set up at first boot:

Approach 1

Don't store recovery phrase (amnesic mode, forgets key when turned off), store it on internal flash (Trezor security model) or encrypted on a separate SD card (only this device will be able to decrypt the file)

Approach 2

Amnesic or store the key on a PIN-protected javacard. Uses MemoryCardApplet for that, requires extension board with the smartcard slot. Javacards have reasonably good hardware security - they are tamper-resistant, detect all kind of glitches and introduce additional countermeasures against sidechannel attacks. But they are running proprietary JavaCardOS. We still can benefit from their security features.

TODO:

• [x] add support for Javacards including secure communication.
• [x] encrypt Bitcoin secret such that it's not stored on the Javacard directly - then the attacker will need to hack both Specter-DIY and Javacard.
• [x] add support for SD card as a secret storage
• [x] merge SDKeyStore and FlashKeyStore to a single class and allow the user to chose what media to save the key to.
• [x] add wipe functionality that effectively works as factory reset
• [x] fix plug-unplug of the smartcard (should reopen channel and prompt for PIN code instead of crashing)

[bitcoinheiro]

This is impressive, great work!