Make improvements on selectBestHost method

[ipr0310]

Is your feature request related to a problem? Please describe.
Current way of selecting the best host is just by finding out which node responds the first API request.

Describe the solution you'd like
We should consider adding validation, it does not handle if the node is syncing

Describe alternatives you've considered
On the new mobile wallet, i make request every 240 seconds for checking out if the node is out of sync

Additional context
API Method https://signum-network.github.io/signumjs/classes/core.chainservice.html#selectbesthost

[ipr0310]

It would be an improvement which will benefit all current wallets