Authenticate user via MetaMask

On https://pheix.org/admin page we have to add option to pass authentication via MetaMask browser extension.

Here is the prototype and demo how it works: https://gitlab.com/pheix-research/auth-with-metamask

Discussion and technical details: #182 (comment 1490543508)

I guess after the pKey is obtained — it's enough to set it as cookie and call refresh function.

Things to keep an eye on:

1. default tab, it will be undefined, so we have to pass or use default one;
2. extend method: it's unable to extend session cause of we have no public key on backend side to sign the transaction.

Progress:

1. Auth & exit: #186 (comment 2144691737)
2. Extend: #186 (comment 2147024045)
3. Items left: #186 (comment 2202421264)
4. Auth with MetaMask mobile: #186 (comment 2216437495)