[wallet] Verify unconfirmed transactions after syncing

Verify the unconfirmed transactions we download against the consensus
rules. This is currently exposed as an extra `verify` feature, since it
depends on a pre-release version of `bitcoinconsensus`.

Closes #352

src/blockchain/compact_filters/mod.rs

@@ -207,6 +207,7 @@ impl CompactFiltersBlockchain {
                 received: incoming,
                 sent: outgoing,
                 confirmation_time: ConfirmationTime::new(height, timestamp),
+                verified: height.is_some(),
                 fee: Some(inputs_sum.saturating_sub(outputs_sum)),
             };