Flow Providers: Non-custodial wallets #28 - Milestone 1 - Lay2 Submission

Flow Providers: Non-custodial wallets - Milestone 1

This PR is for issue #28.

We have complete the design of the wallet.
- Brief introduction of the features we'll cover and how we'll achieve them.
- Details about the architecture of key management and user flow.
- Prospects to the future when we can implement the full version of UniPass on Flow to present a keyless experience for users in an non-custodial way.

Have have you met the milestone requirements?
- Yes
Have you included tests (if applicable)?
- No tests for this milestone
Have you met the contribution guidelines of the repos you have submitted code to (if applicable)?
- No code for this milestone

Is there anything specific you'd like the PoC to know or review for?
- UniPass has one of the best account abstraction design, yet it requires RSA signature verification ability from the Layer1 to make it possible.
- For now we have to use mnemonics as the backup method, which we think is too much for ordinary users.
- We would like to bring an Internet experience also to Flow users, so maybe we can discuss about this feature after we complete this request.
- Introduction ariticle about UniPass: https://medium.com/unipass/unipass-your-universal-crypto-identity-in-metaverse-b8b932f9313f
Are there other references, documentation, or relevant artifices to mention for this PR (ie. external links to justify design decisions, etc.)?
- UniPass adheres to a pure web format, so as to achieve maximum compatibility and cross-platform ability, and significantly reduce user cost with instant access through links.
- We are not compromising on security because of convenience, because we manage the keys through built-in managers of the browsers(SubtleCrypto) and even the devices(Webauthn).