Default to Local Storage

[jribbink]

Currently FCL defaults to sessionStorage. We should change this default to localStorage as this has been a frequent complaint from users/developers. This was initially a security-conscious decision, but in practice it does not completely align with user/developer needs.

Reasons for switching:

• Most major apps on flow use localStorage anyways
• The security concerns re. persistent sessions were only really related to web wallets. These are largely being replaced by extension/mobile wallets
• Web wallets can still define session expiry criteria themselves
• Requiring constant re-authentication introduces lots of fricition in specific scenarios (e.g. Telegram apps, PWAs)