Design and add nightly CI step verifying that the deploy serialization hasn't changed

Casper Ledger App assumes that the serialization representation of the deploy doesn't change. Pasrer logic in Casper Ledger App depends on some internal details of the system (regarding system payments, etc.) and their representation in the Deploy structure. We cannot break this as that would mean our Ledger integration is broken as well.

Add a step in the nightly build for `casper-node` that will (`git`) check out the [`casper-deploy-generator`](https://github.com/casper-ecosystem/casper-deploy-generator) and call `make test-vectors`. The resulting file `output.txt` needs to be cached in the CI for the later comparison. The new `output.txt` should be compared with the cached one (from the previous nightly buidl) and if there are any discrepancies they need to be reported for manual verification.