Upgradeable validation functions (#918)

* upgrade primitives to allow changing validation function

* set up storage schema for old parachains code

* fix compilation errors

* fix test compilation

* add some tests for past code meta

* most of the runtime logic for code upgrades

* implement old-code pruning

* add a couple tests

* clean up remaining TODOs

* add a whole bunch of tests for runtime functionality

* remove unused function

* fix runtime compilation

* extract some primitives to parachain crate

* add validation-code upgrades to validation params and result

* extend validation params with code upgrade fields

* provide maximums to validation params

* port test-parachains

* add a code-upgrader test-parachain and tests

* fix collator tests

* move test-parachains to own folder to work around compilation errors

* fix test compilation

* update the Cargo.lock

* fix parachains tests

* remove dbg! invocation

* use new pool in code-upgrader

* bump lockfile

* link TODO to issue

polkadot/parachain/test-parachains/halt/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "test-parachain-halt"
+version = "0.7.29-pre1"
+authors = ["Parity Technologies <admin@parity.io>"]
+description = "Test parachain which executes forever"
+edition = "2018"
+build = "build.rs"
+
+[dependencies]
+
+[build-dependencies]
+wasm-builder-runner = { package = "substrate-wasm-builder-runner", version = "1.0.5" }
+
+[features]
+default = [ "std" ]
+std = []