* Update libp2p. Add support for ed25519 node (network) keys.

  * Update networking to the changes from https://github.com/libp2p/rust-libp2p/pull/972.
  * Add support for using ed25519 keys for libp2p networking.
  * Add support for reading libp2p secret keys from (external) files.

* Adapt to changes from https://github.com/libp2p/rust-libp2p/pull/992

* More tests.

* Cosmetics

* Deduplicate tests.

* Remove quickcheck from tests that don't use extra random inputs.

* Remove quickcheck.

* Swap new/default impls for NetworkConfiguration.

* Use libp2p-0.5.0 from crates.io.

* Post-rebase update.

* Remove unnecessary wildcard pattern.

* Combine two overlapping tests.