Allow mainchain to switch to different service URL

[ManuGowda]

Expected behavior

When we have more than 1 service URL for mainchain/sidechain, users should be allowed to switch to different service URL.
Also ensure that if one of the service URL is not functioning, remaining URLs are tried to connect and repeat the procedure until we exhaust the list of URL, in the end if none of the URLs are not working, we show users a error message.

Actual behavior

Currently we have the ability to choose a particular sidechain service URL to connect to, however the mainchain can not. If the first entry in service URL is not functioning then the users can not use the mainchain application for any given network.

Steps to reproduce

• Add multiple service URL entries to app registry fro both mainchain and sidechain
• Ensure the first service URL is not up and running and second entry is working
• Observe the mainchain is unable to connect and also unable to probe to second URL