Swap upgrade: allow users to filter allowed exchanges + select from multiple quotes

[justindg]

Two major upgrades:

1. Allow users to select from exchanges via Settings. The available exchanges are available via /tools. In Android, we copied and saved locally + modified to add the exchange website/URL. We then display and link out to this URL to provide the user some more information, as some exchanges are not as popular.

2. Provide quotes from these selected exchanges via /advanced/routes. Note that this is a POST request

After user selects a quote, you can use the exchange key as parameter to the /quote endpoint (&allowExchanges=)

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Please check out Android PR to see UX. Disclaimer: UX is not final - need Tomek's input/approval Link: https://github.com/AlphaWallet/alpha-wallet-android/pull/2835