Allow parachains to send messages (#274)

* Slots module

* Integrate slots

* More drafting

* Minor updates

* Update parachains to use trati

* More build fixes

* Full code now compiles

* Add renew bid function

* Implement calculate_winner

* Warning remove

* Update gitignore

* Test framework

* Tests

* Further testing

* More tests, new parameterisation.

* Fix and new test

* Thread-safe tests

* Test off-boarding and a fix.

* Test onboarding

* Allow late onboarding.

* Another test and fix

* Avoid println in nostd

* Compact representation of paraids

* Introduce documentation.

* Introduce events.

* Additional test and fix

* Additional test

* Tidy up line lengths.

* Remove printlns

* Use later substrate utils.

* Allow parachains to send messages.

* Fix build/test

* Make slots work with latest substrate

* Update runtime/src/slot_range.rs

Co-Authored-By: Robert Habermeier <rphmeier@gmail.com>

* Update runtime/src/slots.rs

Co-Authored-By: Shawn Tabrizi <shawntabrizi@gmail.com>

* Update runtime/src/slots.rs

Co-Authored-By: Shawn Tabrizi <shawntabrizi@gmail.com>

* Polish logic

* Rewind to earlier substrate master

* Remove dead code.

* Fix build

* Update substrate ref to master

* Update to new inherent digests API

* address grumbles

* fix

* Fix a warning.

* Reworded a comment.

* Check that receipt matches expectations

* Add test for final checks

* Split out queuing logic.

* Test final piece of queuing logic

* Fix up docs.

* More docs fixes

polkadot/runtime/src/claims.rs

@@ -172,6 +172,7 @@ impl<T: Trait> ValidateUnsigned for Module<T> {
 					requires: vec![],
 					provides: vec![],
 					longevity: TransactionLongevity::max_value(),
+					propagate: true,
 				}
 			}
 			_ => TransactionValidity::Invalid(INVALID_CALL)
@@ -345,6 +346,7 @@ mod tests {
 					requires: vec![],
 					provides: vec![],
 					longevity: TransactionLongevity::max_value(),
+					propagate: true,
 				}
 			);
 			assert_eq!(