Improve deposit page for coins or tokens on multiple blockchains

**Is your feature request related to a problem? Please describe.**

Tokens like USDT now natively on multiple blockchains. Many other exchanges support deposits on multiple chains. It is good for bitshares-ui to support multiple chains too.

The deposit page of a modern exchange looks like:

As of writing, on bitshares-ui, when depositing USDT, the deposit page looks like:

The legacy deposit page looks like:

And actually the XBTS.io exchange does support multiple chains on their own website:



**Describe the solution you'd like**
Add a drop-down list on the deposit page so that users can choose to deposit on which chain.
Gateway API changes:
* return a list of supported chains when querying a coin/token.
* when querying for deposit address
* if chain name is specified, return deposit address of the specified chain
* if chain name is not specified (this need to be kept for backward compatibility), ideally we need to know which chain it is on

**Describe alternatives you've considered**
/

**Additional context**
> "Improve deposit page to support showing the Blockchain name of deposit address hence some coins or tokens names can co-exist over multiple blockchains"

Start by locating the current deposit page and the gateway flows that query coin details and deposit addresses. Review how the existing single-chain behavior is rendered and how backward compatibility is handled. Done means users can choose a supported chain, see the relevant deposit address and chain, and existing requests without a chain still work.

Written by the indexing model from the issue text.