Upgrade polkadot-sdk v1.3.0 -> 1.6.0

[4meta5]

Closes #92
Closes #39

Notable Changes for polkadotv1.3.0 -> 1.4.0

polkadot-sdk release 1.4.0

1. Removes spurious error emission:

Nov 21 13:37:34.593 ERROR parachain::pvf: 🚨 Your system cannot securely run a validator. 
Running validation of malicious PVF code has a higher risk of compromising this machine.
  - Cannot unshare user namespace and change root, which are Linux-specific kernel security features: not available: Nov 21 13:37:34.582 TRACE parachain::pvf-common: unsharing the user namespace and calling pivot_root worker_kind=check pivot root worker_pid=1562989 worker_dir_path="/tmp/.tmpxnRzK7/check-can-unshare4LXkykVpKt"
mount MS_BIND: No such file or directory (os error 2)
Nov 21 13:37:34.594 ERROR parachain::pvf: In the next release this will be a hard error by default.
     
More information: https://wiki.polkadot.network/docs/maintain-guides-secure-validator#secure-validator-mode

If seen after this upgrade, error log is legit.

2. XCM builder for XCM construction
3. pallet-xcm: enhance reserve_transfer_assets to support remote reserves
4. Add sudo::remove_key
5. Improvements to try-state devex

Notable Changes for polkadotv1.4.0 -> 1.5.0

polkadot-sdk release 1.5.0

1. Small fixes to beefy consensus
2. Extend XCM builders

Notable Changes for polkadotv1.5.0 -> 1.6.0

polkadot-sdk release 1.6.0

1. More XCM logging for easier debugging
2. pallet-assets swap credit
3. Accept Root origin for ensure_sudo

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[ozgunozerk]

Superb documentation, thanks, will be very useful in the future to see what has changed between versions.

I think we can merge this as soon as open conversations are resolved 👍