Kusama CC-2 v0.6.17

Performance and minor bugfix release for Kusama network.

Priority: Medium

This bumps the native runtime to 1018; alterations include:

• Do nothing for zero imbalances (paritytech/substrate#4089) - this ensures that zero slashes and deposits are not recorded as events.
• Additional call to allow Root to add new claims in the claim module.

Other Substrate changes include:

• Do not download blocks too far ahead (paritytech/substrate#4095)
• Sensible limits for known blocks and extrinsics (paritytech/substrate#4094)
• Bumped dependencies (paritytech/substrate#4087)
• Fix sync stalling on moving head (best block) prior to the tip of the chain sometimes (paritytech/substrate#4091)
• Fix console output for slot duration (paritytech/substrate#4085)