Refactor the stats website by using new data structures from the web app.

[octocat512]

In the stats website code, all tokens-related data are identified/classified by the tokens' symbol. I think it makes frontend code requires frontend devs' development time when adding new token/new pair liquidity data. Using tokens' addresses as a key property is logically correct and it helps scalability for the stats website and reduces adding token/pair time.

• Import constants/tokens and constants/pairs files from the web app.
• Use the CurrencyLogo component from the web app instead of using the CurrencyIcon component.
• Refactor all data used tokens' symbol as a key to data structure token address as a key
• Remove tokens' SVG files in this repo. Instead, use the asset repo.

[BennyOptions]

@hetfly has plans to refactor when doing the redesign