backports to beta (#7434)

* Merge pull request #7368 from paritytech/td-future-blocks

Wait for future blocks in AuRa

* Fix tracing failed calls.

* Problem: sending any Whisper message fails

The error is "PoW too low to compete with other messages"

This has been previously reported in #7144

Solution: prevent the move semantics

The source of the error is in PoolHandle.relay
implementation for NetPoolHandle.

Because of the move semantics, `res` variable is in fact
copied (as it implements Copy) into the closure and for
that reason, the returned result is always `false.

* Merge pull request #7433 from paritytech/td-strict-config

Strict config parsing

* Problem: AuRa's unsafeties around step duration (#7282)

Firstly, `Step.duration_remaining` casts it to u32, unnecesarily
limiting it to 2^32. While theoretically this is "good enough" (at 3
seconds steps it provides room for a little over 400 years), it is
still a lossy way to calculate the remaining time until the next step.

Secondly, step duration might be zero, triggering division by zero
in `Step.calibrate`

Solution: rework the code around the fact that duration is
typically in single digits and never grows, hence, it can be represented
by a much narrower range (u16) and this highlights the fact that
multiplying u64 by u16 will only result in an overflow in even further
future, at which point we should panic informatively (if anybody's
still around)

Similarly, panic when it is detected that incrementing the step
counter wrapped around on the overflow of usize.

As for the division by zero, prevent it by making zero an invalid
value for step duration. This will make AuRa log the constraint
mismatch and panic (after all, what purpose would zero step duration
serve? it makes no sense within the definition of the protocol,
as finality can only be achieved as per the specification
if messages are received within the step duration, which would violate
the speed of light and other physical laws in this case).

* Merge pull request #7437 from paritytech/a5-chains-expanse

Remove expanse chain

* Expanse Byzantium update w/ correct metropolis difficulty increment divisor (#7463)

* Byzantium Update for Expanse

Here the changes go. Hope I didnt miss anything.

* expip2 changes - update duration limit

* Fix missing EXPIP-2 fields

* Format numbers as hex

* Fix compilation errors

* Group expanse chain spec fields together

* Set metropolisDifficultyIncrementDivisor for Expanse

* Revert #7437

* Add Expanse block 900_000 hash checkpoint

* Advance AuRa step as far as we can and prevent invalid blocks. (#7451)

* Advance AuRa step as far as we can.

* Wait for future blocks.

* fixed panic when io is not available for export block, closes #7486 (#7495)

* Update Parity Mainnet Bootnodes (#7476)

* Update Parity Mainnet Bootnodes

* Replace the Azure HDD bootnodes with the new ones :)

* Use https connection (#7503)

Use https when connecting to etherscan.io API for price-info

* Expose default gas price percentile configuration in CLI (#7497)

* Expose gas price percentile.

* Fix light eth_call.

* fix gas_price in light client