Implement mechanism to check if API is up, and switch to backup if necessary.

[JJ12880]

GUI should be able to check back-end API to see if it is up, If not, switch to a backup API

zeroclient_gui/ClientApp/components/Global/API.tsx

Line 9 in d4ed106

var public_base: string = "https://smartchain.radiumcore.org/api/public/"