Determine the secure way to store private keys in the user's file system

[npopeka]

Keeping mnemonics or private keys in the browser’s storage is not safe for a number of reasons:

1. The ability to obtain data by sites and applications.
2. Loss of data during data cleansing.
3. The inability to use private mode.

We need to find a way (probably chrome.fileSystem) for storing such data in encrypted form in the user's file system.
Most important link: https://developer.chrome.com/apps/fileSystem

Other links:
https://stackoverflow.com/questions/29355539/google-chrome-extension-save-data-localy

https://stackoverflow.com/questions/37932068/chrome-extension-to-save-data-to-local-file

https://dev.to/aussieguy/reading-files-in-a-chrome-extension--2c03

https://developer.chrome.com/apps/app_storage

https://www.howtogeek.com/255653/how-to-find-your-chrome-profile-folder-on-windows-mac-and-linux/

https://metamask.zendesk.com/hc/en-us/articles/360018766351-How-to-use-the-Vault-Decryptor-with-the-MetaMask-Vault-Data

https://ethereum.stackexchange.com/questions/52658/where-does-metamask-store-the-wallet-seed-file-path

https://stackoverflow.com/questions/17774857/where-is-chrome-extensions-chrome-storage-local-data-saved

https://github.com/MetaMask/metamask-extension/blob/47024fd9a530c1554cfa74c8e74f6221e00c6135/app/scripts/metamask-controller.js

https://developer.chrome.com/apps/storage

[mastercyb]

@Jonybang @npopeka Guys, could you elaborate on your decision?

[mastercyb]

Done