feat(app): basic password authentication

[mrfelton]

Description:

This PR adds basic password authentication for the app. The password is stored in plain text in the indexed database so it's not a strong protection, however it does provide a useful basic level of protection.

This is currently an opt-in feature that users can enable from the preferences page

Additional things we should consider:

1. Store password in more secure way (eg, in the keychain)
2. Require users to enter existing password in order to change password
3. Enable password to grant access to all wallets
4. Auto-lock app after a time limit

Motivation and Context:

Fix #1387

How Has This Been Tested?

Manually

Screenshots (if appropriate):

Types of changes:

Feature

Checklist:

• My code follows the code style of this project.
• I have reviewed and updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes where needed.
• All new and existing tests passed.
• My commits have been squashed into a concise set of changes.

[coveralls]

Coverage increased (+0.2%) to 23.128% when pulling ddabf58 on mrfelton:feat/password into ec0ec28 on LN-Zap:next.

[korhaliv]

Some feedback

[korhaliv]

Some comments

[mrfelton]

Updated

[mrfelton]

Closing in favour of #2940