Allow changing the default session timeout

[gabaldon]

This is a issue created base on #1677

When synchronizing with the blockchain from the start (e.g., after creating a new wallet), Sheikah logs off periodically. This makes sense to have when you are not synchronizing as a feature to protect user funds. However, it's quite annoying when Sheikah logs out mid-synchronization. I recently synchronized a new wallet from 0 and I had to re-login a couple of times before it was finally synced. Unless you constantly keep an eye out for the wallet logging out, you're losing a lot of time because the wallet does not keep synchronizing while logged out (as far as I know) which means you cannot synchronize overnight. I would like to see a user option in the settings menu where one can set a default timeout (e.g., 5 minutes, 30 minutes, 1 hour, never).

[aesedepece]

As far as I know, the wallet keeps synchronizing even if you log out. This is how I keep all my 5+ wallets synced. I log in and log out for all of them at once, and then leave Sheikah running. Moreover, when it automatically logs out, you get a nice message clearly stating that you shouldn't worry, synchronization will continue running in the background.

[aesedepece]

That being said, I support the idea of adjusting the timeout through the settings menu.

[Tommytrg]

Do we need to update witnet-rust wallet code for this?