* aura: remove unneeded SlotDuration struct and rename digest -> digests
* aura: add alias type for SlotDuration
* aura: fix tests
* Fix missing parameters in get_or_compute
* Use special function for fetching aura slot_duration
`GossipEngine` spawns two tasks, one for a periodic tick, one to forward
messages from the network to subscribers. These tasks hold an `Arc` to a
`GossipEngineInner`.
To reduce the amount of shared ownership (locking) this patch integrates
the two tasks into a `Future` implementation on the `GossipEngine`
struct. This `Future` implementation can now be called from a single
owner, e.g. the `finality-grandpa` `NetworkBridge`.
As a side effect this removes the requirement on the `network-gossip`
crate to spawn tasks and thereby removes the requirement on the
`finality-grandpa` crate to spawn any tasks.
This is part of a greater effort to reduce the number of owners of
components within `finality-grandpa`, `network` and `network-gossip` as
well as to reduce the amount of unbounded channels. For details see
d9837d7dd, 5f80929dc and 597c0a6c4.
* Restructure node-template so it is clear that node, runtime, and pallets are separated
* Separating to mock and tests
* restructuring runtime to top-level
* updated release script
* updated Cargo.lock
Robert Habermeier