Discount Confidential Transactions

[dangeross]

This PR:

• Bumps dependencies LWK 0.8.0 (* see issues), elements 0.25.0
• Updates the secp256k1-zkp patch rebasing the original patch on 0.11.0
• Uses Discount CT to calculate fees and takes into account the discount vsize when calculating tx sizes
• Broadcasts txs using the confisured electrum server instead of esplora
• Remove use of esplora to fetch txs & script history

Partially addresses #554 by using Discount-CT instead of lowball fees and removes the requirement to broadcast via the functionaries mempool.

Depends on breez/breez-sdk-greenlight#1151
Fixes #625

Issues
Currently seeing this issue initialising LWK throwing a UpdateOnDifferentStatus error, that I've added into the workaround to clear the persisted storage:

Update created on a wallet with status 4744058033684919366 while current wallet has 17512409250608082394

Looks similar to this issue, but the fix is already applied

[danielgranhao]

Looks good. Left some nit comments.

Regarding the workaround, how much of an overhead does it represent? I'm trying to understand if it's fine to ship it.

[roeierez]

LGTM.

[roeierez]

@dangeross This can be merged now and we can start test it on misty.