In this commit we add a test that demonstrates the problem of ghost
UTXOs lingering in the wallet after a re-scan, even if they were spent.
NOTE: This test shows the incorrect behavior and will be adjusted in a
follow-up commit to show the correct behavior after patching the
btcwallet version.
This commit starts the construction of the new package `lntemp`. This
package serves as the scaffolding while we migrate our old itest into
the new one. Once the migration is finished, the package will be put
back to `lntest`.
