monero: Use fee priority enums from monero repo CLI/RPC wallets (#499)

* monero: Use fee priority enums from monero repo CLI/RPC wallets

* Update processor for fee priority change

* Remove FeePriority::Default

Done in consultation with @j-berman.

The RPC/CLI/GUI almost always adjust up except barring very explicit commands,
hence why FeePriority 0 is now only exposed via the explicit command of
FeePriority::Custom { priority: 0 }.

Also helps with terminology.

---------

Co-authored-by: Luke Parker <lukeparker5132@gmail.com>

processor/src/networks/monero.rs

@@ -761,7 +761,7 @@ impl Network for Monero {
       vec![(address.into(), amount - fee)],
       &Change::fingerprintable(Some(Self::test_address().into())),
       vec![],
-      self.rpc.get_fee(protocol, FeePriority::Low).await.unwrap(),
+      self.rpc.get_fee(protocol, FeePriority::Unimportant).await.unwrap(),
     )
     .unwrap()
     .sign(&mut OsRng, &Zeroizing::new(Scalar::ONE.0))