Improve TDex flow (discovery & tdex registry)

[louisinger]

This PR improves the tdex flow in the app:

• fetch providers (and markets) from registry (use a new Svelte store: tdexstore.ts).
• handle all assets, fetch Infos from explorer (new svelte store: coinstore.ts).
• use Discoverer to select best orders from providers (Trade.svelte).
• use the marina UTXO events to get and delete utxos instead of marina.getCoins call.

it reuses the functions of tdex-app (see utils/tdex.ts file)

Note that this PR does not add support for testnet or regtest (does it make sense on dex.vulpem.com?). And do not add any new "visual elements" like the number of providers/markets available etc... (may be useful ??).

it closes #4

@tiero @bordalix please review

[tiero]

Let's have @bordalix to review as well :)

[bordalix]

ACK.

My only issue is not showing the user the true reason for the error.

[bordalix]

Yes, I also prefer to have all the constants on the same file.