Implement Slashing Protection (#1116)

* Implement slashing protection

Roll-up of #588 with some conflicts resolved

* WIP improvements

* Require slot uniqueness for blocks (rather than epochs)
* Native DB support for Slot and Epoch
* Simplify surrounding/surrounded-by queries

* Implement unified slashing protection database

A single SQL database saves on open file descriptors.

* Make slashing protection concurrency safe.

Revive tests, add parallel tests.

* Some simplifications

* Auto-registration, test clean-ups

* More tests, clean-ups, hardening

* Fix comments in BLS

* Optimise bulk validator registration

* Delete outdated tests

* Use bundled SQLite in slashing protection

* Auto-register validators in simulation

* Use real signing_root in slashing protection

* Update book for --auto-register

* Refine log messages and help flags

* Correct typo in Cargo.toml authors

* Fix merge conflicts

* Safer error handling in sqlite slot/epoch

* Address review comments

* Add attestation test mutating block root

Co-authored-by: pscott <scottpiriou@gmail.com>

validator_client/src/cli.rs

@@ -17,9 +17,19 @@ pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
         .arg(
             Arg::with_name("allow-unsynced")
                 .long("allow-unsynced")
-                .help("If present, the validator client will still poll for duties if the beacon
+                .help("If present, the validator client will still poll for duties if the beacon \
                       node is not synced.")
         )
+        .arg(
+            Arg::with_name("auto-register")
+                .long("auto-register")
+                .help("If present, the validator client will register any new signing keys with \
+                       the slashing protection database so that they may be used. WARNING: \
+                       enabling the same signing key on multiple validator clients WILL lead to \
+                       that validator getting slashed. Only use this flag the first time you run \
+                       the validator client, or if you're certain there are no other \
+                       nodes using the same key.")
+        )
         /*
          * The "testnet" sub-command.
          *