add carbon chain with optimisations

[stevenkhong]

• add Carbon mainnet and testnet chain configs.
• add util function to prioritise chain config assets for default selected token dropdowns.
• add support for KeplrSignOptions through chain configs.
• update chain config readme for KeplrSignOption support.

[liangping]

Hello, @stevenkhong. thanks for PR, We have re-implemented the module that hands inter-operations of txs. And will release in 2-3 days.
The coming release will conflict with your PR more or less. I hope you could merge it and fix conflicts.

If you are interested, You can take a look here: https://github.com/ping-pub/explorer/tree/re-implement-operation-modal

[liangping]

@stevenkhong Hey. Can you solve the conflicts. Let me know when you done it