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>

tests/processor/src/networks.rs

@@ -342,7 +342,7 @@ impl Wallet {
           vec![(to_addr, AMOUNT)],
           &Change::new(view_pair, false),
           data,
-          rpc.get_fee(Protocol::v16, FeePriority::Low).await.unwrap(),
+          rpc.get_fee(Protocol::v16, FeePriority::Unimportant).await.unwrap(),
         )
         .unwrap()
         .sign(&mut OsRng, spend_key)