Improve CoinGecko stability, add attribution

[JSKitty]

Abstract

This simple PR improves the stability of our CoinGecko integration:

• MPW now quietly catches any errors on data refreshes.
• MPW can still display the correct Currency even if CoinGecko is unavailable.
• MPW can fallback to in-memory cache, if CoinGecko suddenly goes unresponsive.

Previously, even a single CoinGecko call failing would still display a generic "Uncaught Network Error" for the user, CoinGecko calls sometimes randomly fail, so this was causing users that kept MPW open for long periods of time, to randomly return to errors on their app, this should be less now that CoinGecko errors are handled perfectly.

Additionally, the PR adds i18n'd CoinGecko attribution, which is required by their documentation terms.

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Testing

This PR is fairly behind-the-scenes, so the best tests a user can do, is to simply check that their currency (USD, GBP, etc) is loading correctly, displaying correctly in all areas, and that the Settings show the currency options and CoinGecko attribution.

For folks that are confident in messing with the Browser Developer Console, however, you can follow this to thoroughly test the PR:

• Load up MPW as normal, login.
• Open the console, hit "Network".
• Find a "CoinGecko" request, and hit "Block URL" or similar depending on your browser.
• Once you've blocked CoinGecko's requests from MPW, watch for any errors, the GUI should NOT show any errors, and prices should continue displaying nicely from local cache, any CoinGecko errors will be silently placed in the Console Logs.

If any errors are found, the PR works unexpectedly, or you have viable suggestions to improve the UX or functionality of the PR, let me know!

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[BreadJS]

This is a lot better than the annoying notifications on fetch error!
Works as expected! Good job Kitty!

LGTM!

[JSKitty]

Tested by another ~2 rewarded Quality Control members, merging PR!